Stan, Roger, Alexander, Thanks for the helpful posts. After posting, I decided to study up a bit on what SATA 3Gb/s actually means. It turns out that the 3Gbit/s bandwidth is aggregate per controller. This is a 4-port SATA controller, so with 1 drive, the single drive gets all 3Gbit/s. With 4 operating simultaneously, each would get 750Mbit/s. There is supposed to be about a 20% overhead involved in the SATA internals, so that number drops to ~600Mbit/s. This is 75MByte/s, which is about what I'm seeing on writes. For reads, I would expect to see ~300MBytes/s, and am seeing 260MBytes/s, which is not too far off. This is not really a problem for me, as the workloads I'm concerned about are seekier than this, and are not bandwidth limited. (e.g. Rebuilding indexes of Cobol C/ISAM files, and it's doing well on that.) Mainly, I just wanted to make sure that this wasn't an indication that I was doing something wrong, and to see if maybe there was something to be learned here (which there was). Bonnie++ does report that the RAID10 is doing ~2x the number of seeks/s as the single-drive configuration. I'll be comparing the results of "iozone -ae" between single-drive and RAID10 later today, to get a more fine-grained view of the relative write performance. BTW Stan, for ext4 stride and stripe-width are specified in filesystem blocks rather than in K. In this case, I'm using the default 4k block size. So stride should be: chunksize / blocksize = 512k / 4k = 128 and the stripe-width should be: stride * number of mirrored sets In this case, I have 2 mirrored sets. So stripe-width should be 128 * 2 = 256. -Steve Bergman On Fri, Jun 7, 2013 at 3:07 AM, Alexander Zvyagin <zvyagin.alexander@xxxxxxxxx> wrote: >> And it is also possible that running more disks at the same time >> cannot be sustained by the on-board chipset. > > to check this, start "dd" or "badblocks" or something similar (which > will put disk to 100% load) on all your drives one-by-one and monitor > throughput with "iostat" (or similar). Yam may face the following > 'problem': > 1. start badblocks on /dev/sda, throughput is 140 MB/s > 2. start badblocks on /dev/sdb, throughput is 140 MB/s on /dev/sda and /dev/sdb > 3. start badblocks on /dev/sdc, throughput is 140 MB/s on /dev/sda and > 70 MB/s on /dev/sdb,/dev/sdc > > Alexander -- 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
