December 2002
Intermediate to advanced
260 pages
9h 18m
English
Content preview from Managing RAID on LinuxBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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RAID-4 (Dedicated Parity)
Since RAID-4 requires that a single drive be dedicated for storing parity information, a minimum of three drives are needed to make RAID-4 useful. Using less than three drives would offer no increase in storage capacity over RAID-1.
A two-drive RAID-4 system would not offer better performance or fault tolerance when compared with RAID-1 or RAID-0. Therefore, in situations in which only two drives are available, RAID-0 or RAID-1 should be used. Furthermore, RAID-5 offers much better performance when compared with RAID-4; almost everyone should choose the former.
The following is a sample RAID-4 configuration using /etc/raidtab:
# RAID-4 with three member disks raiddev /dev/md0 raid-level 4 chunk-size 64 persistent-superblock 1 nr-raid-disks 3 device /dev/sdb1 raid-disk 0 device /dev/sdc1 raid-disk 1 device /dev/sdd2 raid-disk 2
Use mkraid to construct this array:
# mkraid /dev/md0
handling MD device /dev/md0
analyzing super-block
disk 0: /dev/sdb1, 17920476kB, raid superblock at 17920384kB
disk 1: /dev/sdc1, 17920476kB, raid superblock at 17920384kB
disk 2: /dev/sdd1, 17920476kB, raid superblock at 17920384kBOr mdadm:
# mdadm -Cv -l4 -c64 -n3 /dev/md0 /dev/sd{b,c,d}1
mdadm: array /dev/md0 started.When this array is initialized, the last member disk listed in /etc/raidtab, or on the command line using mdadm, becomes the parity disk—/dev/sdd1, in this case. RAID-4 also supports spare disks.
Like other arrays with redundancy, /proc/mdstat will indicate that the initial ...
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