COMPASS Computerized Analysis and Storage Server Iain Last

24 th November 1999 Iain Last, University Of Liverpool Outline  Why?  Hardware  Linux Device Drivers  Linux Installation and Limits  Benchmarking Tests  Results  Future

24 th 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.

24 th 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.

24 th 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  only 16 disks per disk major number.

24 th 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, 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

24 th 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.

24 th November 1999 Iain Last, University Of Liverpool Results: Writing I

24 th November 1999 Iain Last, University Of Liverpool Results: Writing II

24 th November 1999 Iain Last, University Of Liverpool Results: Reading

24 th 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.