> - 2 RAID controllers: ARECA with 7 SATA disks each (RAID5) what are the /sys/block settings for the blockdevs these export? I'm thinking about max*sectors_kb. > - stripe size is always 64k > > Measured with IOMETER (MB/s, 64 kb block size with sequential I/O). I don't see how that could be expected to work well. you're doing sequential 64K IO from user-space (that is, inherently one at a time), and those map onto a single chunk via md raid0. (well, if the IOs are aligned - but in any case you won't be generating 128K IOs which would be the min expected to really make the raid0 shine.) > one HW RAID controller: > - R: 360 W: 240 > two HW RAID controllers: > - R: 619 W: 480 (one IOMETER worker per device) > MD0 over two HW RAID controllers: > - R 367 W: 433 (one IOMETER worker over md device) > > Read throughput is similar to a single controller. Any hint how to > improve that? > Using a larger block size does not help. which blocksize are you talking about? larger blocksize at the app level should help. _smaller_ block/chunk size at the md level. and of course those both interact with the block size prefered by the areca. > We are considering using MD to combine HW RAID controllers with battery > backup support for better data protection. maybe. all this does is permit the HW controller to reorder transactions, which is not going to matter much if your loads are, in fact, sequential. > In this scenario md should do > no write caching. in my humble understanding, MD doesn't do WC. > Is it possible to use something like O_DIRECT with md? certainly (exactly O_DIRECT). this is mainly instruction to the pagecache, not MD. I presume O_DIRECT mainly just follows a write by a barrier, which MD can respect and pass to the areca driver (which presumably also respects it, though the point of battery-backed cache would be to let the barrier complete before the IO...) - 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
