Software RAID issues (was Re: Suggestions solicited, server bring up)

[Alan Johnson]

On Mon, Nov 23, 2009 at 1:09 PM, Tom Buskey <tom at buskey.name> wrote:

>
>
> On Mon, Nov 23, 2009 at 10:31 AM, Alan Johnson <alan at datdec.com> wrote:
> I have a Ubuntu 9.10 box that boots a RAID6 with GRUB2.  I expect that is
> very new, eh?
>
> So your Ubuntu does software RAID6 on the boot disks with / and /boot?
>

Um, certainly /, but now that you mention it, I'm not 100% sure on /boot.
I'm pretty sure it is on there as well, as I don't think I split it out on
this machine, but since it is a critical point, let me get back to you.  I
have that box rolled back to 9.04 now because some video issues I had with
9.10.  Since this is the machine I have hooked to my TV, video is kind of
paramount. =)  It used new drives for the 9.10 upgrade so I just need to
swap them back in to see if anything is fixed yet.  It could have been my
mother board.  It gets flaky when I max out the RAM at 4GB.  I have since
pull it back to 2GB when I was reminded of the issue after going back to
9.04.

Anyway, I'm hoping to get to that over T-day break, so I'll confirm /boot as
well and let you know.


>
> Or you have a hardware RAID card doing RAID6?
>

Linux/mdadm


> I once replaced my 120 GB drives with 500 GB drives to increase the pool.
> It didn't seem slow to me, but..  You'll have to google :-/ to get real
> numbers.  I suspect the speed is similar to RAID 5/6 rebuilds
>

Yes, I've heard that performance is really good while rebuilding and it is
nice to have it confirmed.  However, on a busy system, I expect the trade
off is even longer rebuild times.


> ZFS will work on top of ISCSI SAN drives.  Or you can share out a partion
> from a ZFS pool as an iSCSI target.
>

Now THAT sounds like the stuff!  So, you can make and share ZFS partitions?
Is that functionally similar to LVM partitions?  I'm a bit confused.  More
below...


>
>
> zpool create raidz mypool c0t0d0 c0t1d0 c0t2d0 # create a RAIDZ from 3
> disks
>
> # Create a home with 10GB, max, share it on NFS and compress the data as it
> comes in
> zfs create mypool/home
> zfs set quota=10G mypool/home
> zfs set compression=on mypool/home
> zfs set sharenfs=on mypool/home
>
> # Another one, but put it on iscsi
> zfs create mypool/iSC
> zfs set quota=10G mypool/iSC
> zfs set compression=on mypool/iSC
> zfs set shareiscsi=on mypool/iSC
>
> They really got the CLI stuff right!
>

Nice!  But then what does it look like to the client?  Doesn't iSCSI appear
like a block device that still needs a file system on top of it?  Does the
client need ZFS support?  That's the rub if I want to boot Linux clients
from it. NFS removes the need for ZFS on the client, but I am concerned
about network overhead for some of our heavier needs.


>
>> I'm tempted to try Fuse+ZFS for our database servers, or even just to
>> right to FreeBSD, but
>
>
> I wouldn't touch *anything* FUSE for production work.  Well, I've used
> NTFS-3G because I had to.
>

Yeah, I keep trying to put it out of my head, but it keeps sneaking back in
there.  I know it is not what I want it to be, but I can't stop wanting it!


>
> Get VirtualBox and play with FreeBSD/FreeNAS/Solaris/OpenSolaris inside it.
>

I've got a blade chassis coming out of production after some upgrades in
Q1.  I can use for a lab, so I'm just going to hold off until then so I can
get all the pieces of our production cloud going at once and see what breaks
when I do nutty stuff to get ZFS in the mix.
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