how to setup linux software RAID 10

[Krsnendu dasa]

Does anyone know any of any disadvantages with raid 10?
We have 4 identical SATA 320 GB Hard disks and we were thinking of
using Linux software RAID 10. We actually did it on a trial system and
it seemed to work fine.
We just created 2 raid 1 devices initially and installed edubuntu 7.04
on one of them using LVM and automatic partitioning.

Once we had installed we used mdadm to raid0 the two raid 1 devices together.
When we tried to use Sysrescue CD to copy an image of the root  (/)
partition we ran into some problems. Someone suggested the errors
might be caused by the RAID 10 and advised use to just use RAID 1
(leaving the two extra drives as spares.)

I am not convinced though. It seems like a waste to have 2 extra
drives and not use them to boost performance.

Any thoughts or tips?

Krsnendu dasa


On 26/08/2007, Stefano Rivera <ubuntu-edubuntu-devel at rivera.za.net> wrote:
> Hi Joe (2007.08.25_21:35:38_+0200)
> > My wish list:
> > Step by step instructions, with a FAQ, some screen snapshots etc.
> > Things like, now you have completed this so you should see this...
>
> Every distro is different. These things aren't static. But when you are
> used to it, you know what to do.
>
> Software Raid 10 in linux is rather new, and so probably isn't well
> documented. Personally, I've never used RAID 10, all my servers use RAID
> 1, and if they have lots of disks, RAID 5. (Often system on RAID1, data
> on RAID5) And they use LVM on top of that.
>
> The debian installer (which is on the ubuntu alternate install CDs) does
> software RAID and LVM, and it's easy. The principle to create a RAID
> device is:
> * Create a partition on each drive, and set it's type to RAID.
> * Go into the RAID menu, and create a RAID device out of those
>   partitions.
> * Now on the partitioning screen, you'll see a RAID drive /dev/md* turn
>   it into an LVM PV or a filesystem.
>
> My normal approach is:
> 2 system disks, not massive, but good value for money size, with 2
> partitions on them
> * The first partition is for /dev/md0: maybe 10GB. It houses /
> * The second partition is for /dev/md1: It houses an LVM PV & VG called
>   system.
> * /home is an LV on system
> * swap is an LV on system
> * /usr is an LV on system, if my install grows beyond 10G
> * Anything else special is an LV on system (i.e. /srv/www or /tmp or
>   /var/spool/squid)
> If it's a big server, The rest of the disks contain a single partition
> for RAID5, which is a separate LVM group, data.
>
> > How do I set it up so it boots?
>
> The best approach is to make sure that /boot is readable without
> anything special. So make sure it's part of a RAID1.
>
> If you are using kernels without initrds (which all my debian servers
> do), then you want the whole / to be like that. This also helps with
> recovery.
>
> > Which drives should be paired together?
>
> I don't follow, aren't the drives all identical?
>
> > (Is each SATA drive on its own channel?
>
> Yes. SATA doesn't share channels, unless you use port multipliers (which
> aren't currently supported in Linux, AFAIK, and anyway, the SATA bus has
> enough bandwidth to handle a few drives on each port).
>
> > Do I have to do anything special for swap?
>
> If you want performance, you can create a single swap partition on each
> drive, and just swapon them all. This has no redundancy, i.e. disk goes
> down the server will crash.
>
> More common is to just stick the swap on RAID/LVM like everything else.
>
> SR
>
> --
> Stefano Rivera
>   http://rivera.za.net/
>   H: +27 21 794 7937   C: +27 72 419 8559
>
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