Re: Storage array advice anyone?
- From: Matthew Zito <mzito@xxxxxxxxxxx>
- To: jonathan@xxxxxxxxxxxxxxxxxx
- Date: Fri, 17 Dec 2004 09:04:59 -0500
Well, I'll agree with your later posting that a lot of vendors have
jumped on the virtualization bandwagon and I'll agree that a lot of the
virtualization products offer little or no value. For example, the sun
6320 is described as a virtualizing array, when the real benefit seems
to be that you can span management across several smaller arrays (but
not span storage devices!).
When I'm talking about virtualization, I am talking about using large
numbers of spindles to satisfy I/O, and in better examples, software on
the array to rebalance I/O. In the example you give, its true that one
read could span 8 drives with a huge queue of pending requests, but it
depends on the size of the I/O and the stripe size configured on the
array, like anything else - it seems a little unfair to pick an
arbitrary example and use that as a definitive reason why a technology
is bad.
We can look at the other case - I could have a bunch of RAID-10 volumes
and any given read could span two drives. When I then have 64 I/Os
that are pending against that lone RAID-10 volume, wouldn't I be better
off having those I/Os against 50 disks instead of 14?
And as far as sharing disks, even EMC's RAID-1 implementation splits a
disk into a set of volumes and mirrors them to another drive. There's
always the possibility of spindle contention with any RAID group,
including a RAID-10 volume. How well an array copes with that is a
factor of workload, cache, and the elegance/functionality of the array
OS. Like everything else in the world, quality makes a difference.
That's why I suggested that you vet your vendors heavily.
Thanks,
Matt
--
Matthew Zito
GridApp Systems
Email: mzito@xxxxxxxxxxx
Cell: 646-220-3551
Phone: 212-358-8211 x 359
http://www.gridapp.com
On Dec 17, 2004, at 4:23 AM, Jonathan Lewis wrote:
>
>
> Sorry to come in so late on this one - I've
> had a busy three months, and only just got
> back to reading the mail.
>
> Personally I find the whole 'virtualization' thing a
> complete con-trick.
>
> Sure, I now have a LUN which is really 50
> different spindles - so what good is that if I
> send a 'single read request' and that activates
> eight of them. It only takes 8 requests like
> that and there are 64 reads queued up somewhere,
> and who knows where they might be ? Ask
> Cary Millsap about queueing and unstable
> response times. (Then ask Stephen Barr what
> the minimum and maximum response times were
> for his Parallel Query problem).
>
>
> And another thought - I've got a LUN which
> has 50 different spindles. Using reasonably
> modern discs, that's probably around 4TB of
> spindles. How many other databases are going
> to hitting those spindles ? That's what I asked
> the DBA's at a site recently when there 56GB
> database was on a 4TB SAN. Their S/A was
> insisting that the SAN has no performance issues -
> the database had recorded its first 3-second
> 'db file sequential read' time just fifteen minutes
> after I reset the wait times.
>
> Regards
>
> Jonathan Lewis
>
> http://www.jlcomp.demon.co.uk/faq/ind_faq.html
> The Co-operative Oracle Users' FAQ
>
> http://www.jlcomp.demon.co.uk/seminar.html
> Optimising Oracle Seminar - schedule updated Sept 19th
>
>
>
>
>
> ----- Original Message -----
> From: oracle-l-bounce@xxxxxxxxxxxxx
> [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
> On Behalf Of Matthew Zito
> Sent: Thursday, December 16, 2004 12:54 AM
> To: Oracle-L
> Subject: Re: Storage array advice anyone?
>
> -Virtualization/abstraction of storage objects - when the LUN you are
> sending I/Os to is comprised of chunks from 50 different spindles from
> 10 different RAID-5 groups, the performance is excellent.
>
>
>
> --
> //www.freelists.org/webpage/oracle-l
--
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