Date: Fri, 15 Mar 2013 12:55:52 +0400 From: Dmitry Marakasov <amdmi3@amdmi3.ru> To: hardware@FreeBSD.org Subject: Uneven disk throughput distribution Message-ID: <20130315085552.GD99263@hades.panopticon>
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Hi! Not sure if it's FreeBSD problem, but I thought it won't hurt to write about it. I'm playing with a set of new 3TB Seagate ST3000VX000-1CU166 hard disks. Each disk does 160-180MB/s write throughtput with `dd if=/dev/zero of=/dev/adaX bs=10m`, but when all disks are written to simultaneously, throughput distribution is uneven: ada1: 174032158720 bytes transferred in 1486.316119 secs (117089599 bytes/sec) ada2: 174199930880 bytes transferred in 1487.372522 secs (117119234 bytes/sec) ada3: 172805324800 bytes transferred in 1488.324386 secs (116107299 bytes/sec) ada4: 169376481280 bytes transferred in 1489.353551 secs (113724831 bytes/sec) ada5: 157642915840 bytes transferred in 1490.324518 secs (105777577 bytes/sec) ada6: 112449290240 bytes transferred in 1491.338958 secs (75401564 bytes/sec) I guess that summary performance drop is to be expected due to bus/controller throughput cap, but uneven distribution is strange, and if it may be fixed, it may improve performance of large raid arrays. The system is FreeBSD 9.0 amd64. PS. I've tried the same thing on Debian live system. Similar pattern of throughput drop towards the last disk, however the difference is even worse: 142, 140, 136, 130, 117, 49 MB/s -- Dmitry Marakasov . 55B5 0596 FF1E 8D84 5F56 9510 D35A 80DD F9D2 F77D amdmi3@amdmi3.ru ..: jabber: amdmi3@jabber.ru http://www.amdmi3.ru
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