Re: Storage array advice anyone?

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_at_gridapp.com
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_at_freelists.org 

> [mailto:oracle-l-bounce_at_freelists.org]

> 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.

>

>

>

> --

> http://www.freelists.org/webpage/oracle-l


--
http://www.freelists.org/webpage/oracle-l