gstripe stripe size units?

[Pawel Jakub Dawidek]

On Thu, Sep 23, 2004 at 10:43:42PM -0400, Paul Mather wrote:
+> What are the units for the stripe size argument to gstripe's "-s"
+> option?  E.g., does "gstripe label -s 4096 ..." mean use a stripe size
+> of 4096 bytes; 4096 512-byte blocks; or what?  The man page isn't
+> specific.

Bytes.

+> What is a good suggested value for stripe size?  Does anyone have any
+> empirical results to share?  Does it make sense to split the file system
+> block size over the providers of the stripe when calculating the stripe
+> size to use?  E.g., for a 16 KB block size over two providers, make the
+> stripe size 8 KB.  Or, is geom_stripe I/O done in much larger transfers?
+> (Usually, small transfers are poor for performance, arguing in favour of
+> a larger, rather than smaller, stripe size.)

The best you can do is to just try it. There is a tool for this, which
I wrote for tests like this: src/tools/tools/raidtest/.

If gstripe is running in "fast" mode (kern.geom.stripe.fast=1), size of
stripe could be small, because then, it still sends as large I/O requests
as possible and reorganize the data in memory, but this method consumes
a lot of memory if you want it to be efficient.

-- 
Pawel Jakub Dawidek                       http://www.FreeBSD.org
pjd at FreeBSD.org                           http://garage.freebsd.pl
FreeBSD committer                         Am I Evil? Yes, I Am!
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