Date: Wed, 18 Feb 2004 17:29:06 -0500 From: mi+mx@aldan.algebra.com To: fs@FreeBSD.org, performance@FreeBSD.org Subject: strange performance dip shown by iozone Message-ID: <200402181729.06202@misha-mx.virtual-estates.net>
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Hello! I'm trying to tune the amrd-based RAID5 and have made several iozone runs on the array and -- for comparision -- on the single disk connected to the Serial ATA controller directly. The RAID-based FS was newfs-ed with ``-b 65536'', as it is intended to store very large files. The single-disk FS was newfs-ed with defaults. No softupdates were enabled on either, since those seem to degrade iozone results slightly (iozone reads/writes a single file anyway). The filesystems displayed different performance (reads are better with RAID, writes -- with the single disk), but both have shown a notable dip in writing (and re-writing) speed when iozone used the record lengthes of 128 and 256. Can someone explain that? Is that a known fact? How can that be avoided? The machine is an amd64 running a fresh -current. The disks are 200Gb SATAs. RAID5 consists of 6 of them. Thanks! -mi
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