On Mon, Dec 14, 2015 at 3:02 PM, Mark Knecht <markknecht@xxxxxxxxx> wrote: > > > On Mon, Dec 14, 2015 at 12:55 PM, Dallas Clement > <dallas.a.clement@xxxxxxxxx> wrote: >> >> On Mon, Dec 14, 2015 at 2:40 PM, Mark Knecht <markknecht@xxxxxxxxx> wrote: >> > >> > >> > On Mon, Dec 14, 2015 at 12:14 PM, Dallas Clement >> > <dallas.a.clement@xxxxxxxxx> wrote: >> >> >> >> <SNIP> >> >> >> >> Hi Phil, I ran blktrace while writing with dd to a RAID 5 device with >> >> 12 disks. My chunk size is 128K. So I set my block size to 128K * >> >> (12-2) = 1280k. Here is the dd command I ran. >> > >> > Just curious but for my own knowledge if it's RAID5 why is it 12-2? >> > >> > - Mark >> >> > Just curious but for my own knowledge if it's RAID5 why is it 12-2? >> >> Shouldn't be. It should have been 12-1 or writing 1408k. Boy do I >> feel dumb. Anyhow, when writing this value, no more RMWs. Yay! > > I wasn't going to be so bold as to suggest the RMW's would go away but I'm > glad they did. > > So, now you can presumably gather new data looking at speed and post that, > correct? > > Cheers, > Mark Hmm, I think I may have spoke to soon. I did a speed test using fio this time, same bs=1408k. I see lots of RMWs in the trace this time. I did another larger dd transfer too, and I see some RMWs but not very many - maybe 4 or 5 for a 20GB transfer. It looks like the LBAs are increasing for the writes to the disks. 9,10 2 2816 0.737523948 27410 Q WS 965888 + 256 [dd] 9,10 2 2817 0.737620583 27410 Q WS 966144 + 256 [dd] 9,10 2 2818 0.737630651 27410 Q WS 966400 + 256 [dd] 9,10 2 2819 0.737641625 27410 Q WS 966656 + 256 [dd] 9,10 2 2820 0.737651603 27410 Q WS 966912 + 256 [dd] 9,10 2 2821 0.737662735 27410 Q WS 967168 + 256 [dd] 9,10 2 2822 0.737672709 27410 Q WS 967424 + 256 [dd] 9,10 2 2823 0.737683881 27410 Q WS 967680 + 256 [dd] 9,10 2 2824 0.737693896 27410 Q WS 967936 + 256 [dd] 9,10 2 2825 0.737704484 27410 Q WS 968192 + 256 [dd] 9,10 2 2826 0.737714348 27410 Q WS 968448 + 256 [dd] The dd transfers do seem faster when using bs=1408k. But need to collect some more data. -- 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
