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Hardware RAID versus Software RAID

Hardware RAID versus Software RAID. CSE598D 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

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Hardware RAID versus Software RAID

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  1. Hardware RAID versus Software RAID CSE598D Youngjae Kim February 15, 2007

  2. 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.

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

  4. Linux Software RAID • Supported in 2.6 Linuxkernel series by default • RAID Levels • Linear mode • RAID-0 • RAID-1 • RAID-4 • RAID-5 • Etc. • Hacking the source code • /usr/src/linux/drivers/md/raid0.c (or raid1.c, raid5 …) Application File System Buffer Cache Software RAID Device Driver

  5. Example – RAID1 • Configuration File • /etc/raidtab raiddev /dev/md0 raid-level 1 nr-raid-disks 2 nr-spare-disks 0 persistent-superblock 1 device /dev/sdb6 raid-disk 0 device /dev/sdc5 raid-disk 1 • Initialization • mkraid /dev/md0 • Formatting • mke2fs /dev/md0 • Mounting • Mount –text2 /dev/md0 /mnt/raid0 File System / Buffer Cache /dev/md /dev/sdb6 /dev/sdc5

  6. References • Software-RAID-HOWTO • http://tldp.org/HOWTO/Software-RAID-HOWTO.html • Software RAID Configuration in RedHat Linux • http://www.redhat.com/docs/manuals/linux/RHL-9-Manual/custom-guide/ch-software-raid.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.3ware.com/products/pdf/HWvsSW_111804.pdf

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