Hello, Apologies in advance if this question has been answered before - I perused the archives to no avail. I am experiencing slow linear read from a bare raid6 device, while the underlying drives are capable of saturating their capabilities. I can't seem to find an explanation for this. Regular parallel read from members: =========== Imladris:~# echo 3 > /proc/sys/vm/drop_caches; sleep 3; for d in /dev/sd[abcd] ; do dd if=$d of=/dev/null bs=1M count=2048 & done [1] 13953 [2] 13954 [3] 13955 [4] 13956 Imladris:~# 2048+0 records in 2048+0 records out 2147483648 bytes (2.1 GB) copied, 17.331 s, 124 MB/s 2048+0 records in 2048+0 records out 2147483648 bytes (2.1 GB) copied, 17.5719 s, 122 MB/s 2048+0 records in 2048+0 records out 2147483648 bytes (2.1 GB) copied, 18.47 s, 116 MB/s 2048+0 records in 2048+0 records out 2147483648 bytes (2.1 GB) copied, 18.6834 s, 115 MB/s =========== Same sort of read from array itself: =========== Imladris:~# echo 3 > /proc/sys/vm/drop_caches; sleep 3; dd if=/dev/md6 of=/dev/null bs=1M count=8192 8192+0 records in 8192+0 records out 8589934592 bytes (8.6 GB) copied, 34.9699 s, 246 MB/s =========== I was expecting to see numbers in the neighborhood of 450 MB/s My kernel: linux-image-3.2.0-4-rt-amd64 3.2.32-1 Linux 3.2 for 64-bit PCs, PREEMPT_RT My raid6 parameters: http://paste.debian.net/224887/ My partition alignment: http://paste.debian.net/224888/ (reationale: 4k * 255 * 63, keeps both 4k sector drives aligned and older partition utilities happy) My disk parameters: http://paste.debian.net/224890/ Readaheads: http://paste.debian.net/224892/ Any ideas/suggestions welcome. Cheers -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
