COMPASS

Computerized Analysis and Storage Server

Iain Last

24th November 1999 Iain Last, University Of Liverpool

Outline

Why? Hardware Linux Device Drivers Linux Installation and Limits Benchmarking Tests Results Future

24th November 1999 Iain Last, University Of Liverpool

Why?

Store all the data on disk rather than tape.

Faster access to data than with tape. Run jobs on server containing data.

24th November 1999 Iain Last, University Of Liverpool

Hardware

Dell PowerEdge Server, 450 MHz Pentium III, 256 Mb RAM with 4 internal SCSI disks.

4 PowerVault 1200 Disk Servers each with 8 Ultra Wide SCSI LVD disks.Total > 1Tb disk space

Adaptec Ultra Wide SCSI cards.

24th November 1999 Iain Last, University Of Liverpool

Linux Devices Drivers

Linux Device Drivers: Devices accessed through special files in /dev directory specifying

block or character device and major / minor number pairs. Major number refers to a device driver e.g. 8 is a SCSI disk (see

/usr/src/linux/include/linux/major.h) For disks, minor number refers to disk / partition on disk

e.g. /dev/sda major:8 minor:0 first SCSI disk found on system /dev/sda1 major:8 minor:1 first partition /dev/sda15 major:8 minor:15 last partition on first disk /dev/sdb major:8 minor:16 second SCSI disk found on system

minor numbers are 8-bit i.e. only have values in range 0-255 only 16 disks per disk major number.

24th November 1999 Iain Last, University Of Liverpool

Linux Installation & Limits

RedHat Linux 5.2: Kernel 2.0.x Used at Liverpool and CERN – problem: only one SCSI major

number is defined – maximum of 16 SCSI disks allowed. Kernel “hacking” necessary to register new SCSI major number with

system.

RedHat Linux 6.0: Kernel 2.2.x Defines 8 SCSI major numbers : 8, 65-71- max. 128 SCSI disks. Have to create some special files in /dev by hand – relatively trivial

with mknod

Physical limit of only 4 PCI slots for SCSI cards on motherboard

24th November 1999 Iain Last, University Of Liverpool

Benchmarking Tests

Use CERN sequential IO tests for read / write / calibration.

Calculates average write rate over previous 10 writes Calibration: Comment out write statement and run write tests

again. Read test averages file read for > 10Mb data over previous 10

reads.

Modified version of above calculates averages over the whole file.

24th November 1999 Iain Last, University Of Liverpool

Results: Writing I

24th November 1999 Iain Last, University Of Liverpool

Results: Writing II

24th November 1999 Iain Last, University Of Liverpool

Results: Reading

24th November 1999 Iain Last, University Of Liverpool

Future

Have a 32/64 bit PCI Copper Duplex / Optical Fibre Channel RAID disk to test.

More work needed to understand Linux timings and IO.