On Wed, 2017-02-01 at 11:18 +0300, Timofey Titovets wrote: > so, short results (random read on /dev/sdb on client): > block + /dev/sdb ~ 500 iops (emulate_write_cache=0) > fileio + /dev/sdb ~ 90 iops (emulate_write_cache=0) > fileio + /dev/sdb ~ 90 iops (emulate_write_cache=1) > fileio + /storage/LUN/1 ~90 iops (emulate_write_cache=0) > fileio + /storage/LUN/1 ~90 iops (emulate_write_cache=1) > block + /dev/loop0 ~ 90 iops loop directio=0 > block + /dev/loop0 ~ 500 iops loop directio=0 The address of the LIO mailing list is target-devel@xxxxxxxxxxxxxxx instead of linux-scsi@xxxxxxxxxxxxxxx. Anyway, have you tried to disable readahead on /dev/sdb (blockdev --setra / --setfra)? Readahead can have a significant negative impact on random I/O. There is a heuristic in the kernel for automatically disabling readahead for random I/O but maybe that algorithm did not recognize your workload properly. Bart.
