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Date: Wed, 27 Feb 2008 12:20:19 +0100 From: Tomasz Chmielewski <mangoo@...g.org> To: Theodore Tso <tytso@....edu>, Andi Kleen <andi@...stfloor.org>, LKML <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: very poor ext3 write performance on big filesystems? Theodore Tso schrieb: > On Mon, Feb 18, 2008 at 03:03:44PM +0100, Andi Kleen wrote: >> Tomasz Chmielewski <mangoo@...g.org> writes: >>> Is it normal to expect the write speed go down to only few dozens of >>> kilobytes/s? Is it because of that many seeks? Can it be somehow >>> optimized? >> I have similar problems on my linux source partition which also >> has a lot of hard linked files (although probably not quite >> as many as you do). It seems like hard linking prevents >> some of the heuristics ext* uses to generate non fragmented >> disk layouts and the resulting seeking makes things slow. A follow-up to this thread. Using small optimizations like playing with /proc/sys/vm/* didn't help much, increasing "commit=" ext3 mount option helped only a tiny bit. What *did* help a lot was... disabling the internal bitmap of the RAID-5 array. "rm -rf" doesn't "pause" for several seconds any more. If md and dm supported barriers, it would be even better I guess (I could enable write cache with some degree of confidence). This is "iostat sda -d 10" output without the internal bitmap. The system mostly tries to read (Blk_read/s), and once in a while it does a big commit (Blk_wrtn/s): Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 164,67 2088,62 0,00 20928 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 180,12 1999,60 0,00 20016 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 172,63 2587,01 0,00 25896 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 156,53 2054,64 0,00 20608 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 170,20 3013,60 0,00 30136 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 119,46 1377,25 5264,67 13800 52752 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 154,05 1897,10 0,00 18952 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 197,70 2177,02 0,00 21792 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 166,47 1805,19 0,00 18088 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 150,95 1552,05 0,00 15536 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 158,44 1792,61 0,00 17944 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 132,47 1399,40 3781,82 14008 37856 With the bitmap enabled, it sometimes behave similarly, but mostly, I can see as reads compete with writes, and both have very low numbers then: Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 112,57 946,11 5837,13 9480 58488 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 157,24 1858,94 0,00 18608 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 116,90 1173,60 44,00 11736 440 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 24,05 85,43 172,46 856 1728 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 25,60 90,40 165,60 904 1656 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 25,05 276,25 180,44 2768 1808 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 22,70 65,60 229,60 656 2296 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 21,66 202,79 786,43 2032 7880 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 20,90 83,20 1800,00 832 18000 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 51,75 237,36 479,52 2376 4800 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 35,43 129,34 245,91 1296 2464 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 34,50 88,00 270,40 880 2704 Now, let's disable the bitmap in the RAID-5 array: Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 110,59 536,26 973,43 5368 9744 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 119,68 533,07 1574,43 5336 15760 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 123,78 368,43 2335,26 3688 23376 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 122,48 315,68 1990,01 3160 19920 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 117,08 580,22 1009,39 5808 10104 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 119,50 324,00 1080,80 3240 10808 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 118,36 353,69 1926,55 3544 19304 And let's enable it again - after a while, it degrades again, and I can see "rm -rf" stops for longer periods: Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 162,70 2213,60 0,00 22136 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 165,73 1639,16 0,00 16408 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 119,76 1192,81 3722,16 11952 37296 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 178,70 1855,20 0,00 18552 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 162,64 1528,07 0,80 15296 8 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 182,87 2082,07 0,00 20904 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 168,93 1692,71 0,00 16944 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 177,45 1572,06 0,00 15752 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 123,10 1436,00 4941,60 14360 49416 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 201,30 1984,03 0,00 19880 0 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 165,50 1555,20 22,40 15552 224 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 25,35 273,05 189,22 2736 1896 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 22,58 63,94 165,43 640 1656 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 69,40 435,20 262,40 4352 2624 There is a related thread (although not much kernel-related) on a BackupPC mailing list: http://thread.gmane.org/gmane.comp.sysutils.backup.backuppc.general/14009 As it's BackupPC software which makes this amount of hardlinks (but hey, I can keep ~14 TB of data on a 1.2 TB filesystem which is not even 65% full). -- Tomasz Chmielewski http://wpkg.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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