[linux-lvm] striping efficiency

[linux-lvm] striping efficiency

[Alexy Khrabrov]

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

Re: [linux-lvm] striping efficiency

[Goetz Bock]

On Tue, Feb 18 '03 at 14:57, Alexy Khrabrov wrote:
> 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?
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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Re: [linux-lvm] striping efficiency

[grobe]

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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