Raid 0 stripe size

supermiguel · August 24, 2009, 10:22pm

I have a PERC 5/i card. Im using with it 3 15k rpm HDD's (model: SEAGATE Savvio 15K ST936751SS). Im going to install debian on this array.. and im looking for performance... So what would be the stripe size that i should set this raid 0 into to give me the best performance?

Thanks

pludi · August 25, 2009, 2:13am

In short: don't. RAID 0 gives you no redundancy or fault tolerance. Go with RAID 5 (or maybe RAID 1).

As for the stripe size: Dell suggests 128KB stripes.

abhaymittal003 · August 25, 2009, 2:18am

I agree with pludi,
Better go for Raid 1 or Raid 5 ( for more usable space)

supermiguel · August 25, 2009, 9:47am

i do my backups on a raid 5 (3x500gb)... So this perc 5 card, has 3x 36g (15K) hds in raid 0, and a raid 5 of 3x500gb, where my data is going to go. So?? best stripe for raid 0? 128k?

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any one?

Radar · August 25, 2009, 9:56am

What is the nature of your I/O? Predominantly random? Sequential? If you think it's a mix, then go 64K stripe size to split the difference.

supermiguel · August 25, 2009, 10:20am

mostly i do a bit of programing, web browsing and word preocessing.. So i guess that would be sequential?

Radar · August 25, 2009, 10:33am

Highly random. Mix read and write. 64K or smaller I would say.

mark54g · August 25, 2009, 10:37am

Also, please tell me that your "backups" are also going to another spot other than just a RAID 5 set.

Yes, 32-64K would be good for non sequential (sequential would be something like linear video or audio files). 128K would possibly be ideal if your files are greater than 8MB on average.

However, as others have stated, RAID 0, while improving performance, will actually increase the likelihood of failure from even having 1 drive.

supermiguel · August 25, 2009, 10:49am

yup my "backups" are going into a external 1.5TB... I dont think the OS files are larger than 8MB.. So i guess 32k would be ideal?? i can go as low as 4k

Radar · August 25, 2009, 10:56am

Rather than ideal, I would say sufficient for what you are trying to do. Don't stress too much over that detail. You're striping across 3 drives. Ought to be fast.

supermiguel · August 25, 2009, 11:03am

32K it is then thanks

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and for my raid 5 im using 128

mark54g · August 25, 2009, 12:15pm

You may also want to set, depending on your RAM, a read ahead of say 4MB or more as well as a stride in the file system that matches your work pattern.

supermiguel · August 25, 2009, 12:17pm

i have 8gb of ram... Not sure what u mean

chompy · August 25, 2009, 12:24pm

Are you running 64-bit debian? Why?

supermiguel · August 25, 2009, 12:41pm

yes um running 64bit debian.. Why?? umm what should i use?

chompy · August 25, 2009, 12:46pm

Just curious. Wondering what you needed such firepower for.

supermiguel · August 25, 2009, 12:50pm

the prob is that this was my gaming system... So i was running windows and games at very high FPS but now becaue of shool and work cant play much, so i just wanted to conver this system into a fast linux everyday workstation

mark54g · August 25, 2009, 2:00pm

You can set the amount of caching being done whenever a read is going on, but that will use more RAM.

supermiguel · August 25, 2009, 2:21pm

the perc 5 it self has 512mb of ram.. u have any link giving more info about this?

mark54g · August 25, 2009, 4:45pm

the card may be doing its own read ahead and buffering for you, I am not sure enough about the firmware on the PERC card.

I know that in some cases, especially in software RAID, that a read ahead will increase performance in some cases where you were to do some linear reads and such where you read say 4MB ahead of where the target read is, as that will likely be called and you gather the data more efficiently.