striping efficiency

I'm using a SCSI enclosure with 4 drives to store large files and wonder whether to stripe a single LV spanning them and how to choose the size of the stripe?

Cheers,
Alexy Khrabrov :: www.setup.org :: Age Quod Agis

Don't. Use RAID5 and just don't bother to use striping. Otherwise, when one drive fails all your data will be lost, with no hope to recover it.

OTOH if you insist on striping, than use a stripe size, that fits a few times (3-4) into the cache of your disks. That would allow the SCSI system to issue a "disk 1: get chunk A", "d2: cB", "d3: cC", "d4: cD" and than read the chunks fro the disk's cache while the other drives are still busy fatching the chunks from disk (and there is still space in the cach to request the next chunk before getting the last, and don't forget some space for writing and the disks' house keeping).

If you use XFS just use the chunk size your XFS uses. (and replace chunk with strip size ;-))

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Hi!

OK, me too : RAID5!!!! (I've lost enough disks in my raids to shout here ;-)

But I have my own question here... I am going to stripe across two PVs which are two RAID5s. I want to do that as we are getting a fibrechannel storage, and we want to be able to use two channels. So, I will get /dev/sdc linked to a raid5 at channel A, /dev/sdd at channel B, and with striping, will use bandwith of both channels in one Volume Group.

What stripsize would you recommend here...?

Thank you + CU, Lars.

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