[mythtv-users] Linux software raid question
r-mythtv at thefreemanclan.net
Sat Jun 7 11:32:52 UTC 2008
Johnny Russ wrote:
> I know I
> will need to edit /etc/fstab to make sure everything is getting mounted
> in the right spots. Are there other things that need to be attended to
> when transfering a complete system over to software raid like this?
I somewhat-recently did something very similar to this - I added a few
drives and used the opportunity afforded by the extra space to move the
entire system over to RAID. Here is what I did:
1. Created raid1 boot/root partitions. I made my root partition fairly
small to avoid the waste associated with raid1. About the only actual
files on /root are bin, etc, sbin, lib, and root - about 280MB. Note
that your distro must be pretty good about it puts in these directories
or you'll have bootup problems.
2. The rest of the space on the drives went into one big raid5. I used
lvm to chop that space up into a few partitions - home, portage, var,
video, and "data" (everything else). My logic was to contain anything
that could grow beyond where I'd want it to be, and to be able to use
the right filesystem for each job.
3. I slowly moved and symlinked/mounted files from my running system
into the new one, maybe shutting down one service at a time to do it.
Some of the moves necessitated taking the server out of production, but
I was able to slowly move and test quite a bit of it. I prefer this to
just going single-user, moving tons of data,
4. For the more critical parts of the system I made copies instead of
moves, and set up a grub boot option for both root partitions.
5. Once I was booted up in the new environment and satisfied that all
was well I repartitioned my old drives into a big raid5 and added it to
the lvm volume. I then used pvmove to move my myth video partition to
be located on the older drives. Those drives included some 5400 RPM
drives that shouldn't be a big deal with myth, and putting myth on its
own spindles would tend to reduce head seeking and IOBOUND errors.
The only hard-and-fast rules are that boot MUST be raid1, and root
generally must be as well unless you use an initrd to mount it.
Oh, if you want a fully-fault-tolerant system swap should be on raid as
well. However, there is a bit of a caveat there - if you're using IDE
on consumer-grade hardware there is a good chance that the whole system
will crash if a drive goes out anyway - the bus may not handle having a
half-dead drive on it. Linux itself handles it fine, but if the
motherboard can't talk to your other good drives then that isn't of much
help. Server-grade hardware, SCSI, and SATA are more likely to handle
drive failures more gracefully.
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