Date: Thu, 12 Jun 2008 19:54:37 -0500 From: David Kelly <dkelly@hiwaay.net> To: Kirk Strauser <kirk@strauser.com> Cc: freebsd-questions@freebsd.org Subject: Re: Stripe sizes with gstripe Message-ID: <F67BB207-BA27-4772-A90C-5CB3279F0172@hiwaay.net> In-Reply-To: <200806121521.16237.kirk@strauser.com> References: <200806121521.16237.kirk@strauser.com>
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On Jun 12, 2008, at 3:21 PM, Kirk Strauser wrote: > Does gstripe read an entire stripe at a time? If so, why do that > instead of > just reading a few requested blocks? If not, then is there any > advantage > to large stripes? Apparently it won't read anything larger than your stripe size which defaults to a miserable 4k. Doesn't appear the driver collects multiple pending reads and merges them into one transaction. Don't know if ATA/SATA allows that or not, believe it was called "scatter/gather" in SCSI. Built a gstripe volume a while back and played with various stripe sizes trying to maximize KB/t as shown in "systat -v" during massive file read/writes. A stripe size of 131072 (128k bytes) was the best I could get at about 43 KB/t. About 25 MB/sec each on two drives that are capable of 4x that on a Mac Pro (about 55 MB/sec single drive on inner tracks to 100 MB/sec on outer, reading with md5). Anyway, throughput was terrible with the default 4k stripe. If there is a tuning knob that I have missed, would appreciate being told what. IIRC vinum's default stripe was about 87.5kB and "systat -v" reported transactions of that size. -- David Kelly N4HHE, dkelly@HiWAAY.net ======================================================================== Whom computers would destroy, they must first drive mad.
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