[TriLUG] Ubuntu FakeRAID or Software

[Steve Pinkham]

On 11/04/2010 10:25 AM, Jimmy Dorff wrote:
> matt at noway2.thruhere.net wrote:
>> The only time I ran into problems was when I decided to test the RAID.  I
>> powered down, removed a drive, and restarted.  The server booted just
>> fine
>> on the one drive.  I then repeated the process with the other drive.
>>

Did you let MD sync first? if not, then yes, you would definately cause
corruption this way. "cat /proc/mdstat" to make sure all disks are
synced before pulling one ;-)

> 
> RHEL/Fedora have a weekly cron script called "raid-check" that scrubs
> your disks to detect problems early. Searching found a
> /usr/share/mdadm/checkarray tool for ubuntu, but I haven't used that.
> 

Ubuntu also runs the checkarray weekly via cron.

I've been using MD raid for a while with no problems on a few systems.
I've even used it to reshape from a 2 disk RAID 1 to a 3 and later 4
disk raid5 while online, which is a really neat trick if not for the
faint of heart.

I'd say the only downside to MD softraid for most applications is you
must remember RAID is useful, but not a backup replacement. ;-)  It
really is good enough to make you forget that on occasion.

Note that I don't have much experience with /boot or / on softraid, as I
keep those on a separate non-RAID drive (now a small SSD on most
systems), so there might be problems there I don't encounter.  YMMV ;-)