Red Hat Enterprise Linux 6 Storage Administration Guide.pdf

Red Hat Subject Matter ExpertsJosef BacikKamil Dudka Hans de Goede Doug LedfordDaniel Novotny Nathan Straz David WysochanskiContributors Michael Christ ie Sachin PrabhuRob Evers David Howells David LehmanJeff Moyer Eric Sandeen Mike Snitzer

Red Hat Enterprise Linux 6Storage Administration Guide

Deploying and configuring single-node storage in Red Hat Enterprise Linux6Edit ion 2

Red Hat Enterprise Linux 6 Storage Administrat ion Guide

Deploying and configuring single-node storage in Red Hat Enterprise Linux6Edit ion 2

Josef BacikServer Development Kernel File [email protected] QuotasKamil DudkaBase Operating System Core Services - [email protected] Contro l ListsHans de GoedeBase Operating System [email protected] LedfordServer Development Hardware [email protected] NovotnyBase Operating System Core Services - [email protected] /proc File SystemNathan StrazQuality Engineering QE - [email protected] WysochanskiServer Development Kernel [email protected]/LVM2Michael ChristieServer Development Kernel [email protected] StorageSachin PrabhuSoftware Maintenance [email protected] EversServer Development Kernel Storage

[email protected] StorageDavid HowellsServer Development Hardware [email protected] LehmanBase Operating System [email protected] configuration during installationJeff MoyerServer Development Kernel File [email protected] DisksEric SandeenServer Development Kernel File [email protected], ext4 , XFS, Encrypted File SystemsMike SnitzerServer Development Kernel [email protected]/O Stack and LimitsRed Hat Subject Matter ExpertsContributors

Edited byJacquelynn EastEngineering Content [email protected] DomingoEngineering Content [email protected]

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AbstractThis guide provides instructions on how to effectively manage storage devices and file systemson Red Hat Enterprise Linux 6 . It is intended for use by system administrators with basic tointermediate knowledge o f Red Hat Enterprise Linux or Fedora.

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Table of ContentsPreface

1. Do cument Co nventio ns1.1. Typ o g rap hic Co nventio ns1.2. Pull-q uo te Co nventio ns1.3. No tes and Warning s

2. Getting Help and G iving Feed b ack2.1. Do Yo u Need Help ?2.2. We Need Feed b ack

Chapt er 1 . Overview1.1. What's New in Red Hat Enterp rise Linux 6

File Syst em Encrypt ion (T echnology Preview)

File Syst em Caching (T echnology Preview)

Bt rfs (T echnology Preview)

I/O Limit Processing

ext 4 Support

Net work Block St orage

Part I. File Syst ems

Chapt er 2 . File Syst em St ruct ure and Maint enance2.1. Overview o f Filesystem Hierarchy Stand ard (FHS)

2.1.1. FHS Org anizatio n2.1.1.1. Gathering File System Info rmatio n2.1.1.2. The /b o o t/ Directo ry2.1.1.3. The /d ev/ Directo ry2.1.1.4. The /etc/ Directo ry2.1.1.5. The /l ib / Directo ry2.1.1.6 . The /med ia/ Directo ry2.1.1.7. The /mnt/ Directo ry2.1.1.8 . The /o p t/ Directo ry2.1.1.9 . The /p ro c/ Directo ry2.1.1.10 . The /sb in/ Directo ry2.1.1.11. The /srv/ Directo ry2.1.1.12. The /sys/ Directo ry2.1.1.13. The /usr/ Directo ry2.1.1.14. The /var/ Directo ry

2.2. Sp ecial Red Hat Enterp rise Linux File Lo catio ns2.3. The /p ro c Virtual File System2.4. Discard unused b lo cks

Chapt er 3. Encrypt ed File Syst em3.1. Mo unting a File System as Encryp ted3.2. Ad d itio nal Info rmatio n

Chapt er 4 . Bt rfs4.1. Btrfs Features

Chapt er 5. T he Ext 3 File Syst em5.1. Creating an Ext3 File System

8889

10101011

1 212

1 2

1 2

1 2

1 2

1 2

1 3

1 4

1 515151517171818181818191919202021232324

2 52526

2 727

2 829

T able of Cont ent s

1

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5.1. Creating an Ext3 File System5.2. Co nverting to an Ext3 File System5.3. Reverting to an Ext2 File System

Chapt er 6 . T he Ext 4 File Syst em6 .1. Creating an Ext4 File System6 .2. Mo unting an Ext4 File System

Writ e Barriers6 .3. Resiz ing an Ext4 File System6 .4. Backup ext2/3/4 File Systems6 .5. Resto re an ext2/3/4 File System6 .6 . O ther Ext4 File System Util i ties

Chapt er 7 . G lobal File Syst em 2

Chapt er 8 . T he XFS File Syst em8 .1. Creating an XFS File System8 .2. Mo unting an XFS File System

Writ e Barriers8 .3. XFS Quo ta Manag ement

Set t ing Project Limit s8 .4. Increasing the Size o f an XFS File System8 .5. Rep airing an XFS File System8 .6 . Susp end ing an XFS File System8 .7. Backup and Resto ratio n o f XFS File Systems

Simple Mode for xfsrest ore

Cumulat ive Mode for xfsrest ore

Int eract ive Operat ion8 .8 . O ther XFS File System Util i ties

Chapt er 9 . Net work File Syst em (NFS)9 .1. Ho w NFS Wo rks

9 .1.1. Req uired Services9 .2. p NFS9 .3. NFS Client Co nfig uratio n

9 .3.1. Mo unting NFS File Systems using /etc/fs tab9 .4. auto fs

9 .4.1. Imp ro vements in auto fs Vers io n 5 o ver Vers io n 49 .4.2. auto fs Co nfig uratio n9 .4.3. Overrid ing o r Aug menting Site Co nfig uratio n Files9 .4.4. Using LDAP to Sto re Auto mo unter Map s

9 .5. Co mmo n NFS Mo unt Op tio ns9 .6 . Starting and Sto p p ing NFS9 .7. NFS Server Co nfig uratio n

9 .7.1. The /etc/exp o rts Co nfig uratio n File9 .7.2. The exp o rtfs Co mmand

9 .7.2.1. Using exp o rtfs with NFSv49 .7.3. Running NFS Behind a Firewall

9 .7.3.1. Disco vering NFS exp o rts9 .7.4. Ho stname Fo rmats9 .7.5. NFS o ver RDMA

292930

323334

3435353738

4 0

4 14142

4 343

4 545454646

4 8

4 8

4 849

50505152535454555658596 06 26 36 36 56 66 66 76 86 8

Red Hat Ent erprise Linux 6 St orage Administ rat ion Guide

2

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9 .7.5. NFS o ver RDMA9 .8 . Securing NFS

9 .8 .1. NFS Security with AUTH_SYS and exp o rt co ntro ls9 .8 .2. NFS security with AUTH_GSS

9 .8 .2.1. NFS security with NFSv49 .8 .3. File Permissio ns

9 .9 . NFS and rp cb ind9 .9 .1. Tro ub lesho o ting NFS and rp cb ind

9 .10 . References

Inst alled Document at ion

Useful Websit es

Relat ed Books

Chapt er 1 0 . FS- Cache10 .1. Perfo rmance Guarantee10 .2. Setting Up a Cache10 .3. Using the Cache With NFS

10 .3.1. Cache Sharing10 .3.2. Cache Limitatio ns With NFS

10 .4. Setting Cache Cull Limits10 .5. Statis tical Info rmatio n10 .6 . References

Part II. St orage Administ rat ion

Chapt er 1 1 . St orage Considerat ions During Inst allat ion11.1. Up d ates to Sto rag e Co nfig uratio n During Installatio n11.2. Overview o f Sup p o rted File Systems11.3. Sp ecial Co nsid eratio ns

Separat e Part it ions for /home, /opt , /usr/local

DASD and zFCP Devices on IBM Syst em Z

Encrypt ing Block Devices Using LUKS

St ale BIOS RAID Met adat a

iSCSI Det ect ion and Configurat ion

FCoE Det ect ion and Configurat ion

DASD

Block Devices wit h DIF/DIX Enabled

Chapt er 1 2 . File Syst em Check12.1. Best Practices fo r fsck12.2. Filesystem-Sp ecific Info rmatio n fo r fsck

12.2.1. ext2, ext3, and ext412.2.2. XFS12.2.3. Btrfs

Chapt er 1 3. Part it ions13.1. Viewing the Partitio n Tab le13.2. Creating a Partitio n

6 86 96 9707071717172

7 2

7 3

7 3

7 47575767677787979

8 0

8 18 18 18 2

8 2

8 2

8 3

8 3

8 3

8 3

8 3

8 3

8 58 58 68 68 78 9

9 09 19 2


3

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13.2. Creating a Partitio n13.2.1. Making the Partitio n13.2.2. Fo rmatting and Lab eling the Partitio n13.2.3. Ad d to /etc/fs tab

13.3. Remo ving a Partitio n13.4. Resiz ing a Partitio n

Chapt er 1 4 . LVM (Logical Volume Manager)14.1. What is LVM2?14.2. Using system-co nfig -lvm

14.2.1. Uti l iz ing Uninitialized Entities14.2.2. Ad d ing Unallo cated Vo lumes to a Vo lume Gro up14.2.3. Mig rating Extents14.2.4. Ad d ing a New Hard Disk Using LVM14.2.5. Ad d ing a New Vo lume Gro up14.2.6 . Extend ing a Vo lume Gro up14.2.7. Ed iting a Lo g ical Vo lume

14.3. LVM References

Inst alled Document at ion

Useful Websit es

Chapt er 1 5. Swap Space15.1. Ad d ing Swap Sp ace

15.1.1. Extend ing Swap o n an LVM2 Lo g ical Vo lume15.1.2. Creating an LVM2 Lo g ical Vo lume fo r Swap15.1.3. Creating a Swap File

15.2. Remo ving Swap Sp ace15.2.1. Red ucing Swap o n an LVM2 Lo g ical Vo lume15.2.2. Remo ving an LVM2 Lo g ical Vo lume fo r Swap15.2.3. Remo ving a Swap File

15.3. Mo ving Swap Sp ace

Chapt er 1 6 . Disk Quot as16 .1. Co nfig uring Disk Quo tas

16 .1.1. Enab ling Quo tas16 .1.2. Remo unting the File Systems16 .1.3. Creating the Quo ta Datab ase Files16 .1.4. Assig ning Quo tas p er User16 .1.5. Assig ning Quo tas p er Gro up16 .1.6 . Setting the Grace Perio d fo r So ft Limits

16 .2. Manag ing Disk Quo tas16 .2.1. Enab ling and Disab ling16 .2.2. Rep o rting o n Disk Quo tas16 .2.3. Keep ing Quo tas Accurate

16 .3. Disk Quo ta References

Chapt er 1 7 . Redundant Array of Independent Disks (RAID)17.1. RAID Typ es

Firmware RAID

Hardware RAID

Soft ware RAID17.2. RAID Levels and Linear Sup p o rt

9 29 29 39 39 49 4

9 69 79 7

10 010 110 410 610 710 8110113

1 1 3

1 1 3

1 1 4114115115116116116117117118

1 1 9119119120120121122123123123123124125

1 2 6126

1 2 6

1 2 6

1 2 7127


4

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17.2. RAID Levels and Linear Sup p o rt17.3. Linux RAID Sub systems

Linux Hardware RAID cont roller drivers

mdraid

dmraid17.4. RAID Sup p o rt in the Installer17.5. Co nfig uring RAID Sets

mdadm

dmraid17.6 . Ad vanced RAID Device Creatio n

Chapt er 1 8 . Using t he mount Command18 .1. Lis ting Currently Mo unted File Systems

18 .1.1. Sp ecifying the File System Typ e18 .2. Mo unting a File System

18 .2.1. Sp ecifying the File System Typ e18 .2.2. Sp ecifying the Mo unt Op tio ns18 .2.3. Sharing Mo unts18 .2.4. Mo ving a Mo unt Po int

18 .3. Unmo unting a File System18 .4. mo unt Co mmand References

18 .4.1. Manual Pag e Do cumentatio n18 .4.2. Useful Web sites

Chapt er 1 9 . T he volume_key funct ion19 .1. Co mmand s19 .2. Using vo lume_key as an ind ivid ual user19 .3. Using vo lume_key in a larg er o rg anizatio n

19 .3.1. Prep aratio n fo r saving encryp tio n keys19 .3.2. Saving encryp tio n keys19 .3.3. Resto ring access to a vo lume19 .3.4. Setting up emerg ency p assp hrases

19 .4. vo lume_key References

Chapt er 2 0 . Access Cont rol List s20 .1. Mo unting File Systems

20 .1.1. NFS20 .2. Setting Access ACLs20 .3. Setting Default ACLs20 .4. Retrieving ACLs20 .5. Archiving File Systems With ACLs20 .6 . Co mp atib il i ty with O ld er Systems20 .7. ACL References

Chapt er 2 1 . Solid- St at e Disk Deployment Guidelines21.1. Dep lo yment Co nsid eratio ns21.2. Tuning Co nsid eratio ns

I/O Scheduler

Virt ual Memory

Swap

127129

1 2 9

1 2 9

1 30130130

1 30

1 30131

1 33133133134135136137140141141142142

1 4 3143144145145146146147147

1 4 8148148148149150150151151

1 53153154

1 54

1 54

1 54


5

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Swap

Chapt er 2 2 . Writ e Barriers22.1. Imp o rtance o f Write Barriers

How Writ e Barriers Work22.2. Enab ling /Disab ling Write Barriers22.3. Write Barrier Co nsid eratio ns

Disabling Writ e Caches

Bat t ery- Backed Writ e Caches

High- End Arrays

NFS

Chapt er 2 3. St orage I/O Alignment and Size23.1. Parameters fo r Sto rag e Access23.2. Usersp ace Access

sysfs Int erface

Block Device ioct ls23.3. Stand ard s

AT A

SCSI23.4. Stacking I/O Parameters23.5. Lo g ical Vo lume Manag er23.6 . Partitio n and File System To o ls

ut il- linux- ng's libblkid and fdisk

part ed and libpart ed

File Syst em t ools

Chapt er 2 4 . Set t ing Up A Remot e Diskless Syst em24.1. Co nfig uring a tftp Service fo r Diskless Clients24.2. Co nfig uring DHCP fo r Diskless Clients24.3. Co nfig uring an Exp o rted File System fo r Diskless Clients

Chapt er 2 5. Online St orage Management25.1. Fib re Channel

25.1.1. Fib re Channel API25.1.2. Native Fib re Channel Drivers and Cap ab il ities

25.2. iSCSI25.2.1. iSCSI API25.2.2. iSCSI Targ et Set up

25.3. Pers istent Naming25.3.1. WWID25.3.2. UUID and Other Pers istent Id entifiers

25.4. Remo ving a Sto rag e Device25.5. Remo ving a Path to a Sto rag e Device25.6 . Ad d ing a Sto rag e Device o r Path25.7. Co nfig uring a Fib re-Channel Over Ethernet Interface

25.7.1. Fib re-Channel o ver Ethernet (FCo E) Targ et Set up

1 54

1 55155

1 55155156

1 56

1 56

1 57

1 57

1 58158159

1 59

1 5916 0

1 6 0

1 6 016 016 116 1

1 6 1

1 6 2

1 6 2

1 6 316 316 316 4

1 6 616 616 616 716 816 816 9170171172172173174176177


6

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25.8 . Co nfig uring an FCo E Interface to Auto matically Mo unt at Bo o t25.9 . Scanning Sto rag e Interco nnects25.10 . iSCSI Disco very Co nfig uratio n25.11. Co nfig uring iSCSI O fflo ad and Interface Bind ing

25.11.1. Viewing Availab le iface Co nfig uratio ns25.11.2. Co nfig uring an iface fo r So ftware iSCSI25.11.3. Co nfig uring an iface fo r iSCSI O fflo ad25.11.4. Bind ing /Unb ind ing an iface to a Po rtal

25.12. Scanning iSCSI Interco nnects25.13. Lo g g ing in to an iSCSI Targ et25.14. Resiz ing an Online Lo g ical Unit

25.14.1. Resiz ing Fib re Channel Lo g ical Units25.14.2. Resiz ing an iSCSI Lo g ical Unit25.14.3. Up d ating the Size o f Yo ur Multip ath Device25.14.4. Chang ing the Read /Write State o f an Online Lo g ical Unit

25.14.4.1. Rescanning lo g ical units25.14.4.2. Up d ating the R/W state o f a multip ath d evice25.14.4.3. Do cumentatio n

25.15. Ad d ing /Remo ving a Lo g ical Unit Thro ug h rescan-scsi-b us.sh

Known Issues Wit h rescan- scsi- bus.sh25.16 . Mo d ifying Link Lo ss Behavio r

25.16 .1. Fib re Channel25.16 .2. iSCSI Setting s With d m-multip ath

25.16 .2.1. NOP-Out Interval/Timeo ut

SCSI Error Handler25.16 .2.2. rep lacement_timeo ut25.16 .3. iSCSI Ro o t

Configuring T imeout s for a Specific Session25.17. Co ntro ll ing the SCSI Co mmand Timer and Device Status

Device St at es

Command T imer25.18 . Online Sto rag e Co nfig uratio n Tro ub lesho o ting

Chapt er 2 6 . Device Mapper Mult ipat hing and Virt ual St orage26 .1. Virtual Sto rag e26 .2. DM-Multip ath

Revision Hist ory

Index

17918 118 118 218 318 418 518 518 618 918 919 019 019 119 219 319 319 419 4

1 9 419 419 419 519 5

1 9 619 619 7

1 9 719 7

1 9 8

1 9 819 8

2 0 020 020 0

2 0 2

2 0 4


7

Preface

1. Document Convent ionsThis manual uses several conventions to highlight certain words and phrases and draw attention tospecific pieces of information.

1.1. T ypographic Convent ionsFour typographic conventions are used to call attention to specific words and phrases. Theseconventions, and the circumstances they apply to, are as follows.

Mono-spaced Bold

Used to highlight system input, including shell commands, file names and paths. Also used tohighlight keys and key combinations. For example:

To see the contents of the file my_next_bestselling_novel in your currentworking directory, enter the cat my_next_bestselling_novel command at theshell prompt and press Enter to execute the command.

The above includes a file name, a shell command and a key, all presented in mono-spaced bold andall distinguishable thanks to context.

Key combinations can be distinguished from an individual key by the plus sign that connects eachpart of a key combination. For example:

Press Enter to execute the command.

Press Ctrl+Alt+F2 to switch to a virtual terminal.

The first example highlights a particular key to press. The second example highlights a keycombination: a set of three keys pressed simultaneously.

If source code is discussed, class names, methods, functions, variable names and returned valuesmentioned within a paragraph will be presented as above, in mono-spaced bold . For example:

File-related classes include filesystem for file systems, file for files, and dir fordirectories. Each class has its own associated set of permissions.

Proport ional Bold

This denotes words or phrases encountered on a system, including application names; dialog-boxtext; labeled buttons; check-box and radio-button labels; menu titles and submenu titles. Forexample:

Choose System Preferences Mouse from the main menu bar to launchMouse Preferences . In the Buttons tab, select the Left-handed mouse checkbox and click Close to switch the primary mouse button from the left to the right(making the mouse suitable for use in the left hand).

To insert a special character into a gedit file, choose Applicat ions Accessories Character Map from the main menu bar. Next, choose Search Find from the Character Map menu bar, type the name of the character in the Search field and click Next. The character you sought will be highlighted in the


8

Character Table. Double-click this highlighted character to place it in the Text to copy field and then click the Copy button. Now switch back to your documentand choose Edit Paste from the gedit menu bar.

The above text includes application names; system-wide menu names and items; application-specificmenu names; and buttons and text found within a GUI interface, all presented in proportional boldand all distinguishable by context.

Mono-spaced Bold Italic or Proportional Bold Italic

Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable orvariable text. Italics denotes text you do not input literally or displayed text that changes dependingon circumstance. For example:

To connect to a remote machine using ssh, type ssh [email protected] at ashell prompt. If the remote machine is example.com and your username on thatmachine is john, type ssh [email protected].

The mount -o remount file-system command remounts the named file system.For example, to remount the /home file system, the command is mount -o remount /home.

To see the version of a currently installed package, use the rpm -q packagecommand. It will return a result as follows: package-version-release.

Note the words in bold italics above: username, domain.name, file-system, package, version andrelease. Each word is a placeholder, either for text you enter when issuing a command or for textdisplayed by the system.

Aside from standard usage for presenting the title of a work, italics denotes the first use of a new andimportant term. For example:

Publican is a DocBook publishing system.

1.2. Pull-quote Convent ionsTerminal output and source code listings are set off visually from the surrounding text.

Output sent to a terminal is set in mono-spaced roman and presented thus:

books Desktop documentation drafts mss photos stuff svnbooks_tests Desktop1 downloads images notes scripts svgs

Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows:

static int kvm_vm_ioctl_deassign_device(struct kvm *kvm, struct kvm_assigned_pci_dev *assigned_dev){ int r = 0; struct kvm_assigned_dev_kernel *match;

mutex_lock(&kvm->lock);

match = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head, assigned_dev->assigned_dev_id); if (!match) { printk(KERN_INFO "%s: device hasn't been assigned

Preface

9

before, " "so cannot be deassigned\n", __func__); r = -EINVAL; goto out; }

kvm_deassign_device(kvm, match);

kvm_free_assigned_device(kvm, match);

out: mutex_unlock(&kvm->lock); return r;}

1.3. Notes and WarningsFinally, we use three visual styles to draw attention to information that might otherwise be overlooked.

NoteNotes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note shouldhave no negative consequences, but you might miss out on a trick that makes your life easier.

ImportantImportant boxes detail things that are easily missed: configuration changes that only apply tothe current session, or services that need restarting before an update will apply. Ignoring abox labeled Important will not cause data loss but may cause irritation and frustration.

WarningWarnings should not be ignored. Ignoring warnings will most likely cause data loss.

2. Get t ing Help and Giving Feedback

2.1. Do You Need Help?If you experience difficulty with a procedure described in this documentation, visit the Red HatCustomer Portal at http://access.redhat.com. From the Customer Portal, you can:

Search or browse through a knowledge base of technical support articles about Red Hatproducts.

Submit a support case to Red Hat Global Support Services (GSS).

Access other product documentation.


10

Red Hat also hosts a large number of electronic mailing lists for discussion of Red Hat software andtechnology. You can find a list of publicly available mailing lists athttps://www.redhat.com/mailman/listinfo. Click the name of any mailing list to subscribe to that list orto access the list archives.

2.2. We Need FeedbackIf you find a typographical error in this manual, or if you have thought of a way to make this manualbetter, we would love to hear from you. Please submit a report in Bugzilla: http://bugzilla.redhat.com/against the product Red Hat Enterprise Linux 6.

When submitting a bug report, be sure to mention the manual's identifier: doc-Storage_Admin_Guide

If you have a suggestion for improving the documentation, try to be as specific as possible whendescribing it. If you have found an error, please include the section number and some of thesurrounding text so we can find it easily.

Preface

11

Chapter 1. OverviewThe Storage Administration Guide contains extensive information on supported file systems and datastorage features in Red Hat Enterprise Linux 6. This book is intended as a quick reference foradministrators managing single-node (that is, non-clustered) storage solutions.

The Storage Administration Guide is split into two parts: File Systems, and Storage Administration.

The File Systems part details the various file systems Red Hat Enterprise Linux 6 supports. Itdescribes them and explains how best to utilize them.

The Storage Administration part details the various tools and storage administration tasks Red HatEnterprise Linux 6 supports. It describes them and explains how best to utilize them.

1.1. What 's New in Red Hat Enterprise Linux 6Red Hat Enterprise Linux 6 features the following file system enhancements:

File System Encryption (Technology Preview)It is now possible to encrypt a file system at mount using eCryptfs , providing an encryption layeron top of an actual file system. This "pseudo-file system" allows per-file and file name encryption,which offers more granular encryption than encrypted block devices. For more information about filesystem encryption, refer to Chapter 3, Encrypted File System.

File System Caching (Technology Preview)FS-Cache[1] allows the use of local storage for caching data from file systems served over the network(for example, through NFS). This helps minimize network traffic, although it does not guarantee fasteraccess to data over the network. FS-Cache allows a file system on a server to interact directly with aclient's local cache without creating an overmounted file system. For more information about FS-Cache, refer to Chapter 10, FS-Cache.

Btrfs (Technology Preview)Btrfs[1] is a local file system that is now available. It aims to provide better performance andscalability, including integrated LVM operations. For more information on Btrfs, refer to Chapter 4,Btrfs.

I/O Limit ProcessingThe Linux I/O stack can now process I/O limit information for devices that provide it. This allowsstorage management tools to better optimize I/O for some devices. For more information on this, referto Chapter 23, Storage I/O Alignment and Size.

ext4 Support

[1]


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The ext4 file system is fully supported in this release. It is now the default file system of Red HatEnterprise Linux 6, supporting an unlimited number of subdirectories. It also features more granulartimestamping, extended attributes support, and quota journaling. For more information on ext4, referto Chapter 6, The Ext4 File System.

Network Block StorageFibre-channel over Ethernet is now supported. This allows a fibre-channel interface to use 10-GigabitEthernet networks while preserving the fibre-channel protocol. For instructions on how to set this up,refer to Section 25.7, Configuring a Fibre-Channel Over Ethernet Interface .

[1] This feature is b eing p ro vid ed in this release as a technology preview. Techno lo g y Preview featuresare currently no t sup p o rted und er Red Hat Enterp rise Linux sub scrip tio n services, may no t b efunctio nally co mp lete, and are g enerally no t suitab le fo r p ro d uctio n use. Ho wever, these features areinc lud ed as a custo mer co nvenience and to p ro vid e the feature with wid er exp o sure.

Yo u are free to p ro vid e feed b ack and functio nality sug g estio ns fo r a techno lo g y p review feature b efo reit b eco mes fully sup p o rted . Erratas wil l b e p ro vid ed fo r hig h-severity security issues.

Net work Block St orage

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Part I. File SystemsThe File Systems section explains file system structure followed by two technology previews: eCryptfsand Btrfs. This is followed by the file systems Red Hat fully supports: ext3, ext4, global file system 2,XFS, NFS, and FS-Cache.


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Chapter 2. File System Structure and MaintenanceThe file system structure is the most basic level of organization in an operating system. The way anoperating system interacts with its users, applications, and security model nearly always depends onhow the operating system organizes files on storage devices. Providing a common file systemstructure ensures users and programs can access and write files.

File systems break files down into two logical categories:

Shareable versus unshareable files

Variable versus static files

Shareable files can be accessed locally and by remote hosts; unshareable files are only availablelocally. Variable files, such as log files, can be changed at any time; static files, such as binaries, donot change without an action from the system administrator.

Categorizing files in this manner helps correlate the function of each file with the permissionsassigned to the directories which hold them. How the operating system and its users interact with afile determines the directory in which it is placed, whether that directory is mounted with read-only orread/write permissions, and the level of access each user has to that file. The top level of thisorganization is crucial; access to the underlying directories can be restricted, otherwise securityproblems could arise if, from the top level down, access rules do not adhere to a rigid structure.

2.1. Overview of Filesystem Hierarchy Standard (FHS)Red Hat Enterprise Linux uses the Filesystem Hierarchy Standard (FHS) file system structure, whichdefines the names, locations, and permissions for many file types and directories.

The FHS document is the authoritative reference to any FHS-compliant file system, but the standardleaves many areas undefined or extensible. This section is an overview of the standard and adescription of the parts of the file system not covered by the standard.

The two most important elements of FHS compliance are:

Compatibility with other FHS-compliant systems

The ability to mount a /usr/ partition as read-only. This is especially crucial, since /usr/contains common executables and should not be changed by users. In addition, since /usr/ ismounted as read-only, it should be mountable from the CD-ROM drive or from another machinevia a read-only NFS mount.

2.1.1. FHS Organizat ionThe directories and files noted here are a small subset of those specified by the FHS document. Referto the latest FHS documentation for the most complete information at http://www.pathname.com/fhs/.

2.1 .1 .1 . Gat hering File Syst em Info rmat io nThe df command reports the system's disk space usage. Its output looks similar to the following:

Example 2.1. df command output

Filesystem 1K-blocks Used Available Use% Mounted on/dev/mapper/VolGroup00-LogVol00

Chapt er 2 . File Syst em St ruct ure and Maint enance

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11675568 6272120 4810348 57% / /dev/sda1 100691 9281 86211 10% /bootnone 322856 0 322856 0% /dev/shm

By default, df shows the partition size in 1 kilobyte blocks and the amount of used and availabledisk space in kilobytes. To view the information in megabytes and gigabytes, use the command df -h. The -h argument stands for "human-readable" format. The output for df -h looks similar to thefollowing:

Example 2.2. df -h command output

Filesystem Size Used Avail Use% Mounted on/dev/mapper/VolGroup00-LogVol00 12G 6.0G 4.6G 57% / /dev/sda1 99M 9.1M 85M 10% /boot none 316M 0 316M 0% /dev/shm

NoteIn the above examples, the mounted partition /dev/shm represents the system's virtualmemory file system.

The du command displays the estimated amount of space being used by files in a directory,displaying the disk usage of each subdirectory. The last line in the output of du shows the total diskusage of the directory; to see only the total disk usage of a directory in human-readable format, use du -hs. For more options, refer to man du.

To view the system's partitions and disk space usage in a graphical format, use the Gnome System Monitor by clicking on Applicat ions System Tools System Monitor or using thecommand gnome-system-monitor. Select the File Systems tab to view the system's partitions.The figure below illustrates the File Systems tab.


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Figure 2.1. GNOME System Monitor File Systems tab

2.1 .1 .2 . T he /boot/ Direct o ryThe /boot/ directory contains static files required to boot the system, for example, the Linux kernel.These files are essential for the system to boot properly.

WarningDo not remove the /boot/ directory. Doing so renders the system unbootable.

2.1 .1 .3. T he /dev/ Direct o ryThe /dev/ directory contains device nodes that represent the following device types:

devices attached to the system;

virtual devices provided by the kernel.

These device nodes are essential for the system to function properly. The udevd daemon createsand removes device nodes in /dev/ as needed.

Devices in the /dev/ directory and subdirectories are defined as either character (providing only aserial stream of input and output, for example, mouse or keyboard) or block (accessible randomly, forexample, a hard drive or a floppy drive). If GNOME or KDE is installed, some storage devices areautomatically detected when connected (such as with a USB) or inserted (such as a CD or DVD


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drive), and a pop-up window displaying the contents appears.

Table 2.1. Examples of common f iles in the /dev d irectory

File Descript ion/dev/hda The master device on the primary IDE channel./dev/hdb The slave device on the primary IDE channel./dev/tty0 The first virtual console./dev/tty1 The second virtual console./dev/sda The first device on the primary SCSI or SATA

channel./dev/lp0 The first parallel port./dev/ttyS0 Serial port.

2.1 .1 .4 . T he /etc/ Direct o ryThe /etc/ directory is reserved for configuration files that are local to the machine. It should containno binaries; any binaries should be moved to /bin/ or /sbin/.

For example, the /etc/skel/ directory stores "skeleton" user files, which are used to populate ahome directory when a user is first created. Applications also store their configuration files in thisdirectory and may reference them when executed. The /etc/exports file controls which file systemsexport to remote hosts.

2.1 .1 .5 . T he /lib/ Direct o ryThe /lib/ directory should only contain libraries needed to execute the binaries in /bin/ and /sbin/. These shared library images are used to boot the system or execute commands within theroot file system.

2.1 .1 .6 . T he /media/ Direct o ryThe /media/ directory contains subdirectories used as mount points for removable media, such asUSB storage media, DVDs, and CD-ROMs.

2.1 .1 .7 . T he /mnt/ Direct o ryThe /mnt/ directory is reserved for temporarily mounted file systems, such as NFS file systemmounts. For all removable storage media, use the /media/ directory. Automatically detectedremovable media will be mounted in the /media directory.

ImportantThe /mnt directory must not be used by installation programs.

2.1 .1 .8 . T he /opt/ Direct o ryThe /opt/ directory is normally reserved for software and add-on packages that are not part of thedefault installation. A package that installs to /opt/ creates a directory bearing its name, forexample /opt/packagename/. In most cases, such packages follow a predictable subdirectorystructure; most store their binaries in /opt/packagename/bin/ and their man pages in


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/opt/packagename/man/.

2.1 .1 .9 . T he /proc/ Direct o ryThe /proc/ directory contains special files that either extract information from the kernel or sendinformation to it. Examples of such information include system memory, CPU information, andhardware configuration. For more information about /proc/, refer to Section 2.3, The /proc VirtualFile System .

2.1 .1 .10. T he /sbin/ Direct o ryThe /sbin/ directory stores binaries essential for booting, restoring, recovering, or repairing thesystem. The binaries in /sbin/ require root privileges to use. In addition, /sbin/ contains binariesused by the system before the /usr/ directory is mounted; any system utilities used after /usr/ ismounted are typically placed in /usr/sbin/.

At a minimum, the following programs should be stored in /sbin/:

arp

clock

halt

init

fsck.*

grub

ifconfig

mingetty

mkfs.*

mkswap

reboot

route

shutdown

swapoff

swapon

2.1 .1 .11. T he /srv/ Direct o ryThe /srv/ directory contains site-specific data served by a Red Hat Enterprise Linux system. Thisdirectory gives users the location of data files for a particular service, such as FTP, WWW, or CVS.Data that only pertains to a specific user should go in the /home/ directory.


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NoteThe default httpd install uses /var/www/html for served content.

2.1 .1 .12. T he /sys/ Direct o ryThe /sys/ directory utilizes the new sysfs virtual file system specific to the 2.6 kernel. With theincreased support for hot plug hardware devices in the 2.6 kernel, the /sys/ directory containsinformation similar to that held by /proc/, but displays a hierarchical view of device informationspecific to hot plug devices.

2.1 .1 .13. T he /usr/ Direct o ryThe /usr/ directory is for files that can be shared across multiple machines. The /usr/ directory isoften on its own partition and is mounted read-only. The /usr/ directory usually contains thefollowing subdirectories:

/usr/bin

This directory is used for binaries.

/usr/etc

This directory is used for system-wide configuration files.

/usr/games

This directory stores games.

/usr/include

This directory is used for C header files.

/usr/kerberos

This directory is used for Kerberos-related binaries and files.

/usr/lib

This directory is used for object files and libraries that are not designed to be directlyutilized by shell scripts or users. This directory is for 32-bit systems.

/usr/lib64

This directory is used for object files and libraries that are not designed to be directlyutilized by shell scripts or users. This directory is for 64-bit systems.

/usr/libexec

This directory contains small helper programs called by other programs.

/usr/sbin

This directory stores system administration binaries that do not belong to /sbin/.

/usr/share

This directory stores files that are not architecture-specific.


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/usr/src

This directory stores source code.

/usr/tmp l inked to /var/tmp

This directory stores temporary files.

The /usr/ directory should also contain a /local/ subdirectory. As per the FHS, this subdirectoryis used by the system administrator when installing software locally, and should be safe from beingoverwritten during system updates. The /usr/local directory has a structure similar to /usr/, andcontains the following subdirectories:

/usr/local/bin

/usr/local/etc

/usr/local/games

/usr/local/include

/usr/local/lib

/usr/local/libexec

/usr/local/sbin

/usr/local/share

/usr/local/src

Red Hat Enterprise Linux's usage of /usr/local/ differs slightly from the FHS. The FHS states that /usr/local/ should be used to store software that should remain safe from system softwareupgrades. Since the RPM Package Manager can perform software upgrades safely, it is notnecessary to protect files by storing them in /usr/local/.

Instead, Red Hat Enterprise Linux uses /usr/local/ for software local to the machine. Forinstance, if the /usr/ directory is mounted as a read-only NFS share from a remote host, it is stillpossible to install a package or program under the /usr/local/ directory.

2.1 .1 .14. T he /var/ Direct o rySince the FHS requires Linux to mount /usr/

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