I don't have an answer to this question, but I can say, I've seen a similar surprising result. I ran iozone on various raid configurations of spindle disks . and on a ramdisk. I was surprised to see the ramdisk is only about 50% to 200% faster than the next best competitor in each category. . I don't have any good explanation for that, but I didn't question it too hard. I accepted the results for what they are . the ramdisk performs surprisingly poorly for some unknown reason.
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-boun...@opensolaris.org] On Behalf Of Matt Cowger Sent: Monday, March 08, 2010 8:58 PM To: zfs-discuss@opensolaris.org Subject: [zfs-discuss] terrible ZFS performance compared to UFS on ramdisk (70% drop) Hi Everyone, It looks like I've got something weird going with zfs performance on a ramdisk..ZFS is performing not even a 3rd of what UFS is doing. Short version: Create 80+ GB ramdisk (ramdiskadm), system has 96GB, so we aren't swapping Create zpool on it (zpool create ram..) Change zfs options to turn off checksumming (don't want it or need it), atime, compression, 4K block size (this is the applications native blocksize) etc. Run a simple iozone benchmark (seq. write, seq. read, rndm write, rndm read). Same deal for UFS, replacing the ZFS stuff with newfs stuff and mounting the UFS forcedirectio (no point in using a buffer cache memory for something that's already in memory) Measure IOPs performance using iozone: iozone -e -i 0 -i 1 -i 2 -n 5120 -O -q 4k -r 4k -s 5g With the ZFS filesystem I get around: ZFS (seq write) 42360 (seq read)31010 (random read)20953 (random write)32525 Not SOO bad, but here's UFS: UFS (seq write )42853 (seq read) 100761 (random read) 100471 (random write) 101141 For all tests besides the seq write, UFS utterly destroys ZFS. I'm curious if anyone has any clever ideas on why this huge disparity in performance exists. At the end of the day, my application will run on either filesystem, it just surprises me how much worse ZFS performs in this (admittedly edge case) scenario. --M
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