Re: Solid State Drives
- From: Jeremy Schneider <jeremy.schneider@xxxxxxxxxxxxxx>
- To: mzito@xxxxxxxxxxx
- Date: Fri, 01 May 2009 10:27:42 -0500
We're in the middle of discussions about this too (just had another one
yesterday), and we have started deploying PCIe-based local devices for a
few applications. We don't have an internal consensus yet about
mirroring. Our Engineering group (my group) is currently recommending
to mirror the devices, but I think a few business customers have chosen
not to. Seems that mitigating the risk of data loss isn't always worth
the cost to them.
We are managing them with ASM, so no worries about filesystem block
sizes. And of course, as Matt says, the enterprise-level SSDs do
write-leveling at the hardware level. I'm not sure if anyone's mentioned
yet that there are also power savings with SSD - especially over the
rack of disks needed to get comparable IOPS. But it's still worth
pointing out that right now (as far as I can tell), flash-based SSD is
not significantly more performant than HDD for large sequential write
operations (e.g. redo/archive), especially when taking price into
consideration.
For me, the bigger question is how to best utilize them with currently
shipping Oracle databases. For small databases, you could possible
stick the whole thing on there. (But is it worth the cost?) For larger
databases, it's probably application dependent... redo? temp? undo? hot
datafiles? Unfortunately, my job right now is to try and figure out
best practices and general recommendations which will be read by lots of
application groups as they decide whether or not to use this hardware.
And most of them don't know much about how Oracle works internally... so
we have to provide solid yet basic/general guidance. It's a terrible
predicament really. :)
-Jeremy
Matthew Zito wrote:
>
> Bear in mind that enterprise SSDs are already write-leveled at a
> hardware level. The big optimization for filesystems with enterprise
> SSD is making sure that filesystem blocks are aligned with the same
> block structure as the SSD is using – for cheap SSDs that don’t do
> write leveling, then there’s a lot of CoW optimizations you can do.
> And you would still RAID your disks – write leveling is nice, but it
> doesn’t handle the failure of a controller chip or something similar.
> So you’re never going to get away from that. As far as the upgrade
> path, the lifespan is comparable for a “spinning rust” hard drive.
>
>
>
> Thanks,
>
> Matt
>
--
Jeremy Schneider
Chicago, IL
http://www.ardentperf.com
--
//www.freelists.org/webpage/oracle-l
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