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 Linux kernel 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 Device Driver Software RAID Buffer Cache

5. Example – RAID1 Configuration File –/etc/raidtab raiddev /dev/md0 raid-level 1 nr-raid-disks 2 nr-spare-disks0 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 /dev/md /dev/sdb6/dev/sdc5 File System / Buffer Cache

6. References Software-RAID-HOWTO –http://tldp.org/HOWTO/Software-RAID-HOWTO.htmlhttp://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.htmlhttp://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.pdfhttp://www.adaptec.com/pdfs/raid_soft_v_hard.pdf –http://www.3ware.com/products/pdf/HWvsSW_111804.pdf