Re: some EVMS questions

On 3/17/07, Eric A. Hall <[email protected]> wrote:
>
> Hi guys,
>
> I'm putting together a storage server for NAS and iSCSI purposes and have
> some questions about EVMS please. I've got a box of Raptor 150 ADFD drives
> and a 3Ware 9650SE board which will provide the basic back-end storage.
> Now I'm looking at options for the partitioning to support the server
> opsys, the NAS storage pool, and the multiple iSCSI volumes. It seems that
> the easiest thing to do would be to just make a single massive RAID-6
> volume out of the drives, expose that to EVMS, and then chop it into
> segments for logical drives. Assuming that's the case:

If you're planning on using iscsi for high I/O applications putting
all the drives in a single raid6 is a bad idea. Try not to have more
than two active LUNs on a single array. If you use one large RAID6
array and then export a bunch of LUNs you'll notice horrible I/O when
multiple initiators begin to write/read from the disk, since each
initiator is reading from significantly different areas of the disk.
If you are exporting only one LUN and using the rest for a fileserver,
NFS/Samba, then disregard what I just said.

>
> I understand that EVMS will let me dynamically resize segments, but how
> transparent is this? I assume it will work for the storage and system root
> XFS partitions, and I also assume that it will not work for the iSCSI
> targets (since the partition and filesystem information for those will be
> managed by the requester, not the server).

EVMS will let you resize the segments of LUNS as well. The trick is to
export LVM/LVM2 regions rather than full fledged partitions. I use a
windows initiator and when I run out of space on my exported LUN, I
stop the target software, go in EVMS and expand that region, bring the
target software back up and use the dynamic disk feature of windows.
Also EVMS can expand linux based LUNs, i.e. ext2/3. PLEASE stop the
target software before you expand the regions otherwise you'll corrupt
the segments.

>
> I have read some articles that talk about splitting the large RAID into
> hundreds of small segments and then using those for dynamic resizing. Is
> that really recommended, or just a neat trick?

Just a neat trick. Try to not break up disks in an array into multiple
partitions. It will only degrade performance - stick to using full raw
disks or partitions which use the whole raw disk.

>
> Can grub load a /boot partition off an EVMS volume without needing a lot
> of black magic stuff? I'm going to be using openSUSE 10.2 for this, btw.
> I'm guessing I'll be better off with an unmanaged partition there, and it
> won't really matter if I have the 3Ware card managing the RAID anyway, but
> I'd prefer to use a single partition management interface.

I'm not quite sure what you mean by EVMS volume, but I'll assume you
created LVM/LVM2 regions in EVMS and want to boot from that. If thats
the case then it's pretty easy - Ubuntu server does this by default.

>
> Does EVMS have support for dmraid, or is that inherited from LVM?

>
> Thanks for the help guys

If you look around on the iscsi-target mail archive there is alot of
information: http://www.nabble.com/iSCSI-Enterprise-Target-f4401.html
about similar issues along with possible performance.

>
>
[snip]


-- 
Scott Kaelin
Sitrof Technologies
[email protected]

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