[TriLUG] Ubuntu FakeRAID or Software

[Brian Blater]

On Thu, Nov 4, 2010 at 6:57 PM, John Brier <johnbrier at gmail.com> wrote:
> On Thu, Nov 4, 2010 at 1:29 PM, Brian Blater <brb.lists at gmail.com> wrote:
>> Any one know a good softwareRAID how-to? I've found a few on Google
>> and will use those unless some one can point me to a good definitive
>> how-to.
>
> man mdadm. It actually has really good examples at the bottom. Read
> the manual thoroughly.

I learned a lot from the man page last night. Created /dev/md0 with 4
33GB partitions. After everything was sync'd I formatted the drive and
was able to mount the partition. I felt pretty good about getting this
far so I added the partition to the fstab and rebooted. Well, that
didn't work. It just hung during reboot. Booted with Knoppix and
removed the partition from fstab and was able to boot up just fine.
However, I noticed that the RAID wasn't active any more and so I had
to run mdadm -A --sync. That must be why it hung during boot. What do
you do to get the RAID to be persistant?

One other thing I noticed was that after the reboot and sync the first
drive was removed from the array. I couldn't seem to re-add the
partition back either.

> BTW, for performance reasons with SATA drives you probably want to set
> the stripe size to around 256k. Also don't put LVM on top of RAID
> devices *unless* you are properly aligning the start of the physical
> extents.

I just used the default 64k, so I will look at using 256k also.

>> I will definitely look at the Webmin page for mdadm.
>
> i thought everyone agreed webmin was a security risk?
>
> JB

I guess there can be many issues with Webmin (incorrectly writing
config files etc.) However, in this case the server is internal only
and Webmin at least gave me a chance to look at some things. I ended
up using the CLI for mdadm anyways.

Thanks again for all the help. I'm getting closer to something usable,
but still have a few quirks to work out.
Brian