On Tue, Mar 24, 2009 at 05:01:04PM +0200, Pasi Kärkkäinen wrote: > On Tue, Mar 24, 2009 at 08:21:45AM -0400, John A. Sullivan III wrote: > > > > > > Core-iscsi developer seems to be active developing at least the > > > new iSCSI target (LIO target).. I think he has been testing it with > > > core-iscsi, so maybe there's newer version somewhere? > > > > > > > We did play with the multipath rr_min_io settings and smaller always > > > > seemed to be better until we got into very large numbers of session. We > > > > were testing on a dual quad core AMD Shanghai 2378 system with 32 GB > > > > RAM, a quad port Intel e1000 card and two on-board nvidia forcedeth > > > > ports with disktest using 4K blocks to mimic the file system using > > > > sequential reads (and some sequential writes). > > > > > > > > > > Nice hardware. Btw are you using jumbo frames or flow control for iSCSI > > > traffic? > > > > > Dunno if you noticed this.. :) > > > > > > > > > > > > When you used dm RAID0 you didn't have any multipath configuration, right? > > Correct although we also did test successfully with multipath in > > failover mode and RAID0. > > > > > OK. > > > > What kind of stripe size and other settings you had for RAID0? > > Chunk size was 8KB with four disks. > > > > > Did you try with much bigger sizes.. 128 kB ? > > > > What kind of performance do you get using just a single iscsi session (and > > > thus just a single path), no multipathing, no DM RAID0 ? Just a filesystem > > > directly on top of the iscsi /dev/sd? device. > > Miserable - same roughly 12 MB/s. > > OK, Here's your problem. Was this btw reads or writes? Did you tune > readahead-settings? > > Can paste your iSCSI session settings negotiated with the target? > > > > > > > Sounds like there's some other problem if invidual throughput is bad? Or did > > > you mean performance with a single disktest IO thread is bad, but using multiple > > > disktest threads it's good.. that would make more sense :) > > Yes, the latter. Single thread (I assume mimicking a single disk > > operation, e.g., copying a large file) is miserable - much slower than > > local disk despite the availability of huge bandwidth. We start > > utilizing the bandwidth when multiplying concurrent disk activity into > > the hundreds. > > > > I am guessing the single thread performance problem is an open-iscsi > > issue but I was hoping multipath would help us work around it by > > utilizing multiple sessions per disk operation. I suppose that is where > > we run into the command ordering problem unless there is something else > > afoot. Thanks - John > > You should be able to get many times the throughput you get now.. just with > a single path/session. > > What kind of latency do you have from the initiator to the target/storage? > > Try with for example 4 kB ping: > ping -s 4096 <ip_of_the_iscsi_target> > > 1000ms divided by the roundtrip you get from ping should give you maximum > possible IOPS using a single path.. > > 4 kB * IOPS == max bandwidth you can achieve. > Maybe I should have been more clear about that.. assuming you're measuring 4 kB IO's with disktest, and you have 1 outstanding IO at a time, then the above is max throughput you can get. Higher block/IO size and higher number of outstanding IOs will give you better thoughput. I think CFQ disk elevator/scheduler has a bug that prevents queue depths bigger than 1 outstanding IO.. so don't use that. "noop" might be a good idea. -- Pasi -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
