Andrew Burgess <aab@xxxxxxxxxxx> wrote: > >Question 1: Why didnt the raid sync I/O show up with vmstat? > > I switched to iostat because of similar observations with vmstat. iostat > at least shows you which devices it is looking at and it agrees with > /proc/mdstat's numbers in my experience. Right. > >Question 2: Why was it limited to 17 MB per second? The maximum was > >left at the default, 200 MB/s. The min was also at the default, 1 MB/s. > >I get 60 MB/s per disk with "hdparm -tT" (that's using one disk at a time, > >but still). The checksumming code does > 3 GB/s. > > Try using dd to read each device in parallel as it might be a bus or controller > limitation. Also, sync requires writing interspersed with the reads which > unavoidably ruins the total throughput. Larger stripes should minimize this if > you think it'll be a problem during everyday use. Before creating the raid, I ran "badblocks -n" (non-destructive read-write mode) on all 4 disks in parallel, and I was getting about 14 MB/s read & 14 MB/s write, per disk, with iostat reporting device utilizations around 97% on all disks. "badblocks" (read-only test) on all 4 in parallel reads ~56 MB/s per disk, call it ~220 MB/s total, with device utilizations again up around 98%. Not bad! I'll just call it sync access pattern overhead then. The disks are Seagate Barracuda 7200.9 500 GB SATA-II. The controller card is a Sonnet Tempo-X 8 SATA, based on the Marvell 6081 chipset. It's a 64-bit/133-MHz PCI-X card plugged in to a 64-bit/66-MHz PCI-X slot, so the limiting factor is the bus, which runs at about 500 MB/s. I should be able to hang eight 60 MB/s disks off this card and still not run into any I/O bottlenecks. :-) -- Sebastian Kuzminsky - 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
