Re: install Etch with raid level 10
Scott Lair <scott@lairhome.com> writes:
> C M Reinehr wrote:
>> On Wednesday 26 September 2007 11:53, Gilles Mocellin wrote:
>> > Le Wednesday 26 September 2007 16:48:14 Scott Lair, vous avez écrit :
>> > Instead of having md over md device, I suggest to do stripped LVM over RAID
>> > 1. And it is supported during installation !
>>
>> Damn! That's a good idea. I'm kicking myself for not thinking of that.
>>
>> cmr
>
> I wish I would have thought of it - LVM was staring me in the face last night!
> Sounds like RAID-10 and LVM/RAID-1 are functionally equivalent. I didn't know
> LVM did stripping. I'm wondering now what the performance difference might be
> if any.
>
> thanks,
>
> scott
You should do some speed tests first. raid1+0 (or lvm stripes) behave
differently to raid10 in its different layouts.
Raid1+0 / Raid10 near copies:
Each block is copied to the same position on another disk. Reading in
a single thread will only use one drive of the mirror. Two threads
will use both though.
Raid10 offset copies:
Not sure what exactly happens but it is no good. I don't see any plus
for offset copies.
Raid 10 far copies:
Think of this as having the following setup:
md0 raid1: sda1 + sdb2
md1 raid1: sdb1 + sdc2
md2 raid1: sdc1 + sdd2
md3 raid1: sdd1 + sda2
md4 raid0: md0 md1 md2 md3
Now writing will have to seek far for each write but it seems to write
sufficiently large chunks per seek to not be noticeable for linear
access.
Reading on the other hand will only use one part of each mirror (sd*1)
but all 4 drives giving you 4 times the drive speed instead of 2 times
like usual raid1+0. But use raid10 instead of doing this manaualy
because otherwise the different raid1s would interfere with each other
performance wise.
In conclusion. I would seriously consider raid10 over raid1+lvm.
MfG
Goswin
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