raid

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cat /proc/mdstat

In following result, md2 shows [UU_], one drive in the raid is not functioning properly, it is recovering. This can be caused by hardware problem.

[[email protected] ~]# cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4]
md0 : active raid1 sdc1[2] sda1[0] sdb1[1]
      6291444 blocks super 1.0 [3/3] [UUU]

md1 : active raid1 sdc2[2] sda2[0] sdb2[1]
      524276 blocks super 1.0 [3/3] [UUU]

md2 : active raid5 sdc3[3] sda3[0] sdb3[1]
      2916638720 blocks super 1.0 level 5, 512k chunk, algorithm 2 [3/2] [UU_]
      [============>........]  recovery = 60.6% (884434512/1458319360) finish=209.6min speed=45630K/sec

unused devices: <none>
[[email protected] ~]#
[[email protected] ~]# mdadm --detail /dev/md2
/dev/md2:
        Version : 1.0
  Creation Time : Wed Mar 20 04:00:24 2013
     Raid Level : raid5
     Array Size : 2916638720 (2781.52 GiB 2986.64 GB)
  Used Dev Size : 1458319360 (1390.76 GiB 1493.32 GB)
   Raid Devices : 3
  Total Devices : 3
    Persistence : Superblock is persistent

    Update Time : Wed Mar 20 11:04:23 2013
          State : clean, degraded, recovering
 Active Devices : 2
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 1

         Layout : left-symmetric
     Chunk Size : 512K

 Rebuild Status : 60% complete

           Name : rescue:2
           UUID : 7aaf9fb2:2699e2be:05a74e1f:96dd453d
         Events : 4130

    Number   Major   Minor   RaidDevice State
       0       8        3        0      active sync   /dev/sda3
       1       8       19        1      active sync   /dev/sdb3
       3       8       35        2      spare rebuilding   /dev/sdc3
[[email protected] ~]#



RAID 10

  • Hardware RAID 10 is where you don't see down time for a single failed drive while maintaining speed. Don't use raid 5 it is slow.
  • For high disk I/O and database server RAID 10 is must for both performance and safety.
  • I do web hosting and every machine I have runs Raid-10 with 250GB SATA Drives. I have lost a drive on almost every machine I have and some machines more than one. With the SL boxes they are hot-swap so there is no down time to replace the bad drive. I primarily use it for i/o though but the fact it means less down time is great as well.
  • You need 4 drives for RAID 10
  • RAID - 10 has 4x read and 2xwrite speed of normal drive (+ SAS / SCSI has higher rpm). So you get good throughput.

Source: https://forums.softlayer.com/showthread.php?t=3840 (customers only)


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