keep accepting write requests. Otherwise you'll just hit the same
on the quantity of data that you are writing. I also can't advise you on
which SSD to buy. Maybe someone on the ZFS discuss list can help there.
> indeed.... you are correct, learning something everyday.
>
> So, how do i get the most out of it? (or is it the most i can get out of
> it?)
>
> In reality, the prime task is to run two linux pv VMs each configured
> similar to the one i am testing with, and use them as the database servers.
> They do not have to be "real" enterprise grade, but they should still be
> able to keep up if I am pumping a few million rows into them everyday. I did
> the initial testing with DB2 9.7 linux, and what i noticed was that after a
> few hours of activity, I tend to have a rather sluggish system. If I stop
> the connecting applications, the disks would still keep showing heavy
> activity for upto 10 to 15 minutes. That's what led me to believe something
> was wrong in the way I was working on it.
>
> This is a just a lab setup which I use for my own craving, but I would want
> it to be a little bit faster than what is right now. Also, I would want the
> data stored in it to be safe from durability point of view.
>
> What would you suggest to get past this bottleneck?
>
> If required, on the hardware side, I am thinking on the lines of adding some
> more similar sized disks for the primary pool, adding three SSDs, one for
> zfs cache and the other two for mirrored zil. Or one SSD for zil and 2
> 10Krpm raptors for cache. Although, I dont really know if database's IO will
> cause any synchronous writes to the zfs pool. Running dd with oflag=sync
> under dom0, does show zil usage (used zilstat script), but running the same
> dd under domU does not show any synchronous usage on zfs, which makes me
> think that the SSD for zil may not be of much help.
>
> Plus, I am also thinking about moving the disks from AOC-SAT2-MV8 PCI-X to
> AOC-USAS-L8i LSI 1068E UIO SAS/SATA PCIE card, just in case PCI-X is adding
> to the slowness.
>
> >From what I have read on the net sofar, the "real" enterprise grade SSDs are
> pricey, mostly because of the capacitor/backup feature or SLC technology.
>
> Can someone also guide me on which SSD would be reasonable enough for this
> task, and if I really should opt for one?
>
> Thanks a lot, do appreciate your help.
>
> Regards,
> dot.yet
>
>
> On Fri, Oct 30, 2009 at 12:45 PM, Stu Maybee <
Stuart.Maybee@...> wrote:
>
> >
> > Since it's a linux domU I would expect to see caching in the domU iirc ext3
> > (or whatever) is a heavily caching fs.
> >
> > Stu
> >
> > Mark Johnson wrote:
> >
> >>
> >>
> >> Gary Pennington wrote:
> >>
> >>> Some answers below...
> >>>
> >>> The above command returns under 2.5 seconds, however iostat on domU AND
> >>>> zpool iostat on dom0, both continue to show write IO activity for upto
> >>>> 30 to
> >>>> 40 seconds:
> >>>>
> >>>
> >> If the domU is showing IO activity, then it must be caching too.
> >>
> >>
> >> When you write the data to the zvol most of the writes are cached
> >>> to memory and the writes to disk are performed later when ZFS writes
> >>> the memory cache to disk. It seems that your logging device is capable
> >>> of writing about 40MB/s (see your figure below), so it takes at least
> >>> 800/20
> >>> seconds to write this to disk.
> >>>
> >>
> >> you can to do a iostat -x 1 and see the stats for
> >> slog device.
> >>
> >>
> >>
> >>
> >> MRJ
> >>
> >> _______________________________________________
> >> xen-discuss mailing list
> >>
xen-discuss@...
> >>
> >
> >
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