Hardware RAID versus Software RAID CSE 598 D

Hardware RAID versus Software RAID CSE 598 D Youngjae Kim February 15, 2007

Hardware RAID vs. Software RAID • Hardware RAID – Not flexible – Fast • RAID subsystem is independent from host system. • Better performance than Software RAID – Expensive • Built-in RAID controller in hardware • Software RAID – Flexible, cheap – Easy to implement RAID • Implemented in kernel disk (block device) code – Performance dependent on host system (CPU and Memory) • Consumes around 25% of host system processing cycles • But, fast CPU help improve the performance of Software RAID.

Performance Comparison http: //www. adaptec. com/pdfs/raid_soft_v_hard. pdf

Linux Software RAID • Supported in 2. 6 Linux kernel series by default • RAID Levels – – – Linear mode RAID-0 RAID-1 RAID-4 RAID-5 Etc. • Hacking the source code Application File System Buffer Cache Software RAID Device Driver – /usr/src/linux/drivers/md/raid 0. c (or raid 1. c, raid 5 …)

Example – RAID 1 • Configuration File – /etc/raidtab raiddev /dev/md 0 raid-level 1 nr-raid-disks 2 nr-spare-disks 0 persistent-superblock 1 device /dev/sdb 6 raid-disk 0 device /dev/sdc 5 raid-disk 1 • Initialization – mkraid /dev/md 0 • Formatting – mke 2 fs /dev/md 0 • Mounting – Mount –text 2 /dev/md 0 /mnt/raid 0 File System / Buffer Cache /dev/md /dev/sdb 6 /dev/sdc 5

References • Software-RAID-HOWTO – http: //tldp. org/HOWTO/Software-RAID-HOWTO. html • Software RAID Configuration in Red. Hat Linux – http: //www. redhat. com/docs/manuals/linux/RHL-9 -Manual/custom-guide/ch-softwareraid. html • Linux source codes for hacking – /usr/src/linux/drivers/md/ • Hardware RAID versus Software RAID – – http: //www. adaptec. com/pdfs/raid_soft_v_hard. pdf http: //www. 3 ware. com/products/pdf/HWvs. SW_111804. pdf