change stripe unit size?

[zzz123456]

Hello.

Has anybody experience with changing the stripe unit size on an existing server?

There is a file-server (IBM x232 using a ServeRaid-4mx with 32 KB stripe-size in both raid5-arrays, one internal raid5 and one external raid5) where i'd like to change the stripe-unit size to increase performance.

After booting the serve-raid CD (updating the firmware to 7.xxx) changing the stripe unit size seems possible.
I just hesitated to do to it because i dont know
- Will this erase the contents?
- How long will it take? Theres 500 GB data I dont wont to restore.
- Is there an effect at all (performance-wise)?

We have other servers (using other ServeRaid-Adapters) doing database-server and other stuff so any information will be helpful.

Thank you.

 

[ibmtech65]

Well you can probably could do it but it would be risky.

If you have 500GB worth of data I would not do it unless it is absolutly necessary. The performance gain would be minimal.

The only way you would get any performance gain would be to lower the stripe size to 8k which is the default.

 

[technome]

Not sure with the IBM hardware, but many raid adapters allow stripe size changes with raid types not involving parity.

Eg Lsilogic adapters..

http://web2.minasi.com/forum/topic.asp?TOPIC_ID=15312&SearchTerms=stripe,size

........................................
Chernobyl disaster..a must see pictorial

http://www.kiddofspeed.com/default.htm

 

[ibmtech65]

To follow up, yes you can do it but only from a higher stripe size to a lower stripe size and you must do it by booting to a servraid manager CD.

Again it is risky and if you really want to do it make sure you have a verified good backup of your data. No specific time frame on how long it will take but with 500GB it will not be a quick process.

 

[zzz123456]

Hi.

> The only way you would get any performance gain would be to lower the stripe size to 8k which is the default.

This is what I plan(ned) to do.

But maybe its better to buy a new file server, but this won't happen in the next six months or so.

The database server still has a "wrong" stripe-size but until now its only 10% full and the cpu is doing nothing all the time. I just dont want it to become a problem.

Only open question now is:
- How often did you do change the stripe-size with with brand of adapter and how often failed it?

Thank you for now.

Totty

 

[technome]

Generally you don't change stripe sizes mid stream if you have been around raid a while. For the most part the default stripe size is the best choice unless you have a server dedicated to a database or a particular file type/size. If you plan on using a size other than the default, it should be tested in a lab atmosphere before placing the server into production. Testing changes to raid setups properly is tedious..multiple benchmarks, testing on the same volume, testing between volumes, tests over the network, copy tests, read and write benches, I/O tests etc.
With the adapters I have used, never lost an array on a stripe change, lab or production. Be aware, during a stripe change, especially with parity, all the blocks will be accessed..should your array adapter have problem reading multiple blocks during the change you will have a problem, I would advise running an array check to test for any problems before any changes; run a full system backup.


........................................
Chernobyl disaster..a must see pictorial

http://www.kiddofspeed.com/default.htm