RAM Disk

[Duffs]

Hi,

Has anyone ever created a virtual disk using RAM (RAM disk)? I'am anxious to try this as I think it should improve my db performance but I can't seem to find any definitite procedure for it.

Rgds,
Dermot

[Pete Randall]

Dermot,

Patrick points out several good reference threads in this thread:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=35625


Pete

[Duffs]

Thanks Pete,

That has effectively answered my query. I'll try the suggested method of procedure for this and see how it goes.

Rgds,
Dermot

[Zinky]

Dermot,

As an alternative AND if you have a large "cache-centric" array attached to your servers - you can ask from whoever manages your arrays if they can carve for you what's called a "Cache-LUN". Cache-LUN is a feature of newer arrays from EMC, HDS (XP line) and I believe IBM. What it does is it allocates a portion of the arrays massive cache as a LUN which does not involve any physical disk.. purely memory. If you're servers are on 2Gbps FC links then such cache LUNs are very good RDBMS acclerators. And safer too as opposed to RAMDISKS which are volatile.

[Duffs]

Nelson,

As I work in a VA environment your recommendation on this (cache-LUN) is a great pointer. I'll have to look into this on a test server and note the db performance differences.

Thanks,
Dermot

[Zinky]

I am not familiar with the VA but arrays I've worked with -- specially the XP line (aka Hitachi Ligtning) where one of my boxen has a 128GB Cache - I've managed to carve a couple of Cache LUNs to serve my RDBMS/Apps fast disk requirements.

There are also Solid State Disks available on the market with either a SCSI or FC connection that may also be an option.

[Ted Buis]

http://www.faqs.org/faqs/hp/hpux-faq/section-81.html has a good discussion.

Also, JTL PlUS product can work with MirrorDisk if I remember correctly, so you can have the RAM disk but also output to disk, which can help with some read intensive senarios.

[Dave Wherry]

Here was a discussion on solid state disk devices:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=134174

Dave

[Tim Sanko]

Nelson you deserve 11 points for this. Thanks!

Tim

[Zinky]

Solid State disks (RAIDed for that matter) or Array Cache LUNS - are the biggest little secret to accelrating applications that truly need them.

[Ted Buis]

What about the cost of cache in the arrays or solid state "disks" compared to server RAM? If you can get enough RAM in the server, wouldn't that be better in some cases?

[Zinky]

Server memory can be corrupted.. and are volatile.

Cache Memory on High-End arrays are mirrored and LUNs carved from it can be treated like any normal disk.

Solid state disks (and arrays) while expensive - do offer the most performance.

[Duffs]

Case closed,
Thanks for the pointers,
D