FreBSD 9.1 and ZFS v28 performances

[Damien Fleuriot]

On Mar 18, 2013 5:39 PM, <kpneal at pobox.com> wrote:
>
> On Mon, Mar 18, 2013 at 03:31:51PM -0000, Steven Hartland wrote:
> >
> > ----- Original Message -----
> > From: "Davide D'Amico" <davide.damico at contactlab.com>
> > To: <freebsd-fs at freebsd.org>
> > Sent: Monday, March 18, 2013 2:50 PM
> > Subject: FreBSD 9.1 and ZFS v28 performances
> >
> >
> > > Hi all,
> > > I'm trying to use ZFS on a DELL R720 with 2x6-core, 32GB ram, H710
> > > controller (no JBOD) and 15K rpm SAS HD: I will use it for a mysql 5.6
> > > server, so I am trying to use ZFS to get L2ARC and ZIL benefits.
> > >
> > > I created a RAID10 and used zpool to create a pool on top:
> > >
> > > # zpool create DATA mfid3
> > > # zpool add DATA cache mfid1 log mfid2
> > >
> > > I have a question on zfs performances. Using:
> > >
> > > dd if=/dev/zero of=file.out bs=16k count=1M
> > >
> > > I cannot go faster than 400MB/s so I think I'm missing something; I
> > > tried removing zil, removing l2arc but everything is still the same.
>
> The ZIL only helps with synchronous writes. This is something apps must
> request specifically typically and I would guess that dd would not do
that.
> So the ZIL doesn't affect your test.
>
> The L2ARC is a read cache. It does very little for writes. If the ZFS
cache
> working set fits all in memory then the L2ARC does nothing for you. Since
> you are writing the only thing needed from the ARC is metadata.
>
> > > mfiutil show volumes:
> > > mfi0 Volumes:
> > >   Id     Size    Level   Stripe  State   Cache   Name
> > >  mfid0 (  278G) RAID-1      64k OPTIMAL Disabled <BASE>
> > >  mfid1 (  118G) RAID-0      64k OPTIMAL Disabled <L2ARC0>
> > >  mfid2 (  118G) RAID-0      64k OPTIMAL Disabled <ZIL0>
> > >  mfid3 ( 1116G) RAID-10   64k OPTIMAL Disabled <DATA>
> > >
> > > zpool status:
> > >   pool: DATA
> > >   state: ONLINE
> > >   scan: none requested
> > > config:
> > >
> > > NAME        STATE     READ WRITE CKSUM
> > > DATA        ONLINE       0     0     0
> > >   mfid3     ONLINE       0     0     0
> > > logs
> > >   mfid2     ONLINE       0     0     0
> > > cache
> > >   mfid1     ONLINE       0     0     0
>
> Warning: your ZIL should probably be mirrored. If it isn't, and the drive
> fails, AND your machine takes a sudden dive (kernel panic, power outage,
> etc) then you will lose data.
>

How so ?
Unless he loses the zil device itself, I can't see how he'd lose pending
trasnsactions.


> > DATA  primarycache          metadata               local
> > DATA  secondarycache        all                    default
>
> Is there a specific reason that you are making a point of not putting
> regular data in the ARC? If you do that then reads of data will look in
> the L2ARC, which is a normal 15k drive, before hitting the main pool
drives
> which also consists of normal 15k drives. Adding an extra set of spinning
> rust before accessing your spinning rust doesn't sound helpful.
>
> > HEAD has some significant changes for the mfi driver specifically:-
> > http://svnweb.freebsd.org/base?view=revision&revision=247369
> >
> > This fixes lots off bugs but also enables full queue support on TBOLT
> > cards so if your mfi is a TBOLT card you may see some speed up in
> > random IO, not that this would effect your test here.
>
> I believe the H710 is a TBOLT card. It was released with the 12G servers
> like the R720.
>

That's a negatory, we've got r[4-7]10 servers here with h710 raid cards.




> I don't believe the OP mentioned how many drives are in the RAID10. More
> drives ~== more parallelism ~== better performance. So I too am wondering
> how much performance is expected.
>
> > While having a separate ZIL disk is good, your benefits may well be
> > limited if said disk is a traditional HD, better to look at enterprise
> > SSD's for this. The same and them some applies to your L2ARC disks.
>
> Before purchasing SSD's check the H710 docs to make sure they are allowed.
> The 6/i in my R610 specifically says that if an SSD is used it must be the
> only drive. Your R720's H710 is much newer and thus may not have that
> restriction. Still, checking the documentation is cheap.
>
> --
> Kevin P. Neal                                http://www.pobox.com/~kpn/
>
> "It sounded pretty good, but it's hard to tell how it will work out
> in practice." -- Dennis Ritchie, ~1977, "Summary of a DEC 32-bit machine"
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