Date: Fri, 13 Jun 2008 09:00:03 -0500 From: Kirk Strauser <kirk@strauser.com> To: FreeBSD Questions <questions@freebsd.org> Cc: freebsd-questions@freebsd.org Subject: Re: Stripe sizes with gstripe Message-ID: <200806130900.04230.kirk@strauser.com> In-Reply-To: <F67BB207-BA27-4772-A90C-5CB3279F0172@hiwaay.net> References: <200806121521.16237.kirk@strauser.com> <F67BB207-BA27-4772-A90C-5CB3279F0172@hiwaay.net>
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[-- Attachment #1 --] 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 [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- iD8DBQBIUn1k5sRg+Y0CpvERAugsAJ45Zrb8PFmjEgllkqgC5LN4SrfliACeJS8q 3crRJeZbYwKEP7geX6PShdM= =KFNB -----END PGP SIGNATURE-----
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