A Few Linux RAID Disk Monitoring Tips

Hey there,

For today's post, I thought I'd put together a few Linux RAID disk monitoring tips. This list isn't meant to be too specific, but more of a catch-all of stuff you probably have to do over and over again. But sometimes not often enough that it burns into your brain ;)

At the very basic level, you can manage your disk partitions using fdisk, much like in Windows, although completely different (type "m" to get a menu listing of available commands once you bring this little utility up). You can use the "-l" option to just print out the partition menu and not use it in interactive mode:

host # fdisk -l /dev/hda 

Disk /dev/hda: 16 heads, 63 sectors, 77520 cylinders 
Units = cylinders of 1008 * 512 bytes 

   Device Boot    Start       End    Blocks   Id  System 
/dev/hda1   *         1      6095   3071848+  fd  Linux raid autodetect 
/dev/hda2          6096     67047  30719808   fd  Linux raid autodetect 
/dev/hda3         67048     73142   3071880   fd  Linux raid autodetect
/dev/hda4         75175     77206   1024096+  82  Linux swap

If you want to display the status of your RAID devices, much the way metastat does on Solaris, it's much simpler. One of the great things about Linux is the way they've taken the /proc filesystem and turned into a really useful tool.

Entering the following will display the information you need. Note that this is a two way mirror with only one active mirror (I take the examples I can find on our network ;). Ideally, you'd want to have a [2/2] configuration for better HA.

host # cat /proc/mdstat

Personalities : [raid1]
read_ahead 1024 sectors
md2 : active raid1 hda3[0]
     62912 blocks [2/1] [U_]

md1 : active raid1 hda2[0]
     153152 blocks [2/1] [U_]

md0 : active raid1 hda1[0]
     307328 blocks [2/1] [U_]

If you're syncing up your RAID devices and want to check on the progress, just use the same command, like so:

host # cat /proc/mdstat 
Personalities : [raid1] 
read_ahead 1024 sectors 
md2 : active raid1 hdc3[1] 
      1020032 blocks [2/1] [_U] 
      
md0 : active raid1 hdc1[1] 
      3068288 blocks [2/1] [_U]
      
md1 : active raid1 hda2[2] hdc2[1] 
      3068288 blocks [2/1] [_U] 
      [==>..................]  recovery = 13.7% (894298/6136576) finish=10.2min speed=7833K/sec 
unused devices: 

Now, assuming all that is taken care of and you want to check out your RAID configuration, you'll just need to read your RAID configuration table (/etc/raidtab):

host # cat /etc/raidtab

raiddev             /dev/md0
raid-level                  1
nr-raid-disks               2
chunk-size                  64k
persistent-superblock       1
nr-spare-disks              0
   device          /dev/hda1
   raid-disk     0
   device          /dev/hdc1
   raid-disk     1
raiddev             /dev/md1
raid-level                  1
nr-raid-disks               2
chunk-size                  64k
persistent-superblock       1
nr-spare-disks              0
   device          /dev/hda2
   raid-disk     0
   device          /dev/hdc2
   raid-disk     1
raiddev             /dev/md2
raid-level                  1
nr-raid-disks               2
chunk-size                  64k
persistent-superblock       1
nr-spare-disks              0
   device          /dev/hda3
   raid-disk     0
   device          /dev/hdc3
   raid-disk     1

If you want to get more detailed with your analysis, there are (of course) built in commands to enable you to do so. lsraid is one of my favorites :)

To display a short listing of the md0 device, type the following:

# lsraid -A -a /dev/md0
[dev 9, 0] /dev/md0 8F88ACB0.7D06B4C4.FA677344.C3448700 online
[dev 3, 3] /dev/hda1 8F88ACB0.7D06B4C4.FA677344.C3448700 good
[dev 22, 3] /dev/hdc1 8F88ACB0.7D06B4C4.FA677344.C3448700 good

If you'd like to display a short listing of the RAID array that the disk hda1 belongs to (essentially the same output in this case), just type:

# lsraid -A -d /dev/hda1
[dev 9, 0] /dev/md0 8F88ACB0.7D06B4C4.FA677344.C3448700 online
[dev 3, 3] /dev/hda1 8F88ACB0.7D06B4C4.FA677344.C3448700 good
[dev 22, 3] /dev/hdc1 8F88ACB0.7D06B4C4.FA677344.C3448700 good

lsraid also comes in handy if you want to list out any faulty devices. This is something to consider putting in cron, or running regularly, so that you get notified of any failures in a timely fashion. No sense in having RAID's HA setup if you wait for all the components to fail before you replace any of them ;)

For a short listing, go with:

# lsraid -A -f -a /dev/md0
[dev 9, 0] /dev/md0 8F88ACB0.7D06B4C4.FA677344.C3448700 online

If you want, or need, all the gruesome details, lsraid will be happy to oblige. Just invoke it like this:

lsraid -D -l -a /dev/md0 
[dev 3, 3] /dev/hda1: 
        md version              = 0.90.0 
        superblock uuid         = 8F88ACB0.7D06B4C4.FA677344.C3448700 
        md minor number         = 0 
        created                 = 1169715493 (Fri Jan 25 08:58:13 2007) 
        last updated            = 1169933481 (Sun Jan 27 21:31:21 2007) 
        raid level              = 1 
        chunk size              = 64 KB 
        apparent disk size      = 3068288 KB 
        disks in array          = 2 
        required disks          = 2 
        active disks            = 2 
        working disks           = 2 
        failed disks            = 0 
        spare disks             = 0 
        position in disk list   = 0 
        position in md device   = 0 
        state                   = good 

[dev 22, 3] /dev/hdc1: 
...

In a near future post (maybe tomorrow), we'll follow up with some tips on setting up your RAID arrays in Linux and walk through that process together.

Hope this helps you out some in the meantime :)

Cheers,

, Mike

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