Stripe sizes with gstripe

[Kirk Strauser]

On Thursday 12 June 2008, David Kelly wrote:

> Apparently it won't read anything larger than your stripe size which
> defaults to a miserable 4k.

Ugh.  It seems like there are a few possibilities here, and I'm not sure 
which is actually true.

Say you have two drives, striped.

1) Ideally, you could have a 512 byte stripe size.  A program tries to read 
4KB.  Then, gstripe would issue a single request to each drive to read 4 
blocks and interleaves the results.

2) Less ideally, you'd have a 128KB stripe size.  A program requests a 
single block, but gstripe reads the entire stripe to fulfill the request.  
Not so hot for random access.

3) Worst, maybe?  You have a 512 byte stripe.  A program reads 4KB.  gstripe 
reads 512B from da0, then 512B from da1, then 512B from da0, etc.

Actually, I guess you could also have a combination of #2 and #3, where 
small reads fetch an entire stripe while large reads are broken into lots 
of tiny ones.

So, back to gstripe.  Which of those is it most like?

> If there is a tuning knob that I have missed, would appreciate being
> told what.

Pass it along, would ya?  :-)

Oh, and don't forget to make your partition offsets
-- 
Kirk Strauser
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