Hi, On 9 January 2014 23:26, Sergey Meirovich <rathamahata@xxxxxxxxx> wrote: > Hi Duglas, > > On 9 January 2014 21:54, Douglas Gilbert <dgilbert@xxxxxxxxxxxx> wrote: >> On 14-01-08 08:57 AM, Sergey Meirovich wrote: > ... >>> >>> The strangest thing to me that this is the problem with sequential >>> write. For example the fnic one machine is zoned to EMC XtremIO and >>> had results: 14.43Mb/sec 3693.65 Requests/sec for sequential 4k. The >>> same fnic machine perfrormed rather impressive for random 4k >>> 451.11Mb/sec 115485.02 Requests/sec >> >> >> You could bypass O_DIRECT and use ddpt together with >> a bsg pass-through (bsg is a little faster than sg >> for these purposes). >> >> For example: >> >> # lsscsi -g >> [0:0:0:0] disk ATA INTEL SSDSC2CW12 400i /dev/sda /dev/sg0 >> [14:0:0:0] disk Linux scsi_debug 0004 - /dev/sg1 >> >> # ddpt if=/dev/bsg/14:0:0:0 bs=512 bpt=128 count=1m >> Output file not specified so no copy, just reading input >> 1048576+0 records in >> 0+0 records out >> time to read data: 0.283566 secs at 1893.28 MB/sec >> >> bs= should match the block size of the storage device and >> the size of each SCSI READ is dictated by bpt= (so 64 KB >> in this case). >> >> Such a test should show you if your performance problem >> is in the block layer or below, or above the block layer >> (at least the point where pass-through commands are >> injected). >> >> Doug Gilbert > > Thanks for an excellent idea! > > Seems like this is not Direct IO issue.Just tried it against > fnic/XtremIO. 4k over via bsg is still 17.278 Mb/s for write. At a second glance seems to be natural ddpt - is suffering from the same SAN latencies for the small chunks. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
