On 2010-03-20, Andres Migliazzo <[email protected]> wrote:
>
> You can always partition the second disk, create a small partition and put
> the mlog in there, for example:
<snip>
> but this setup is not recommended, at least for me. i recommend 3 disks to
> create a LVM mirror.
> What if the /dev/sdb disk fails?
> You loose the information and the mirror log.
Yes, what happens then? We have:
/dev/sda1 => /boot
/dev/sda2 => rootvg
Will add /dev/sdb with same partitioning:
/dev/sdb1 => /manual-copy-of-boot
/dev/sdb2 => rootvg
Put the mlog in rootvg (on sda2).
If /dev/sdb fails, we should have no problem. If /dev/sda fails, for the
mirroring that shouldn't be any worse than an in-memory/corelog. Right?
We'll need a manual routine to boot fram /dev/sdb1 instead of /dev/sda1,
but do we also need a manual routine to get the mirrored lv's with missing
mlog active ?
>
> To be honest I don't recomend you lvm mirror, it is only helpful when you
> have hardware failures.
To survive hardware failures is the reason we want to mirror..
>
> My recommendation for two disk setup is to use pure MD devices. Plus you
> will gain in performance because it reads in parallel and as far as I
> understand LVM2 raid 1 does not.
Unfortunately this machine is already installed, in production and can max
hold 2 drives (it's an IBM ls22 blade). I don't see any other options than
lvm-mirroring.. We'll there is also hw mirroring, but AFAIK it woun't allow
us to convert from single disk to mirrored pair and contain all data..
-jf
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