I asked about this same problem about a month ago and got no answer (http://sourceforge.net/mailarchive/forum.php?thread_id=9277720&forum_id=40837)...
Try watching your vmstat output while doing a copy. Run the command "vmstat 1" and watch the "bi" (block in) and "bo" (blocks out) lines. These are a reflection of actual data delivered from/to the i/o system (anything cached will not show up as a bi or bo). For me it was showing a lot of blocks in (reads) during a iscsi write operation (about 1 read per every ISCSI write packet). This results in slow performance since it interrupts the harddisk write stream.
I don't know if your problem is the same, but if it is I have yet to find a solution and so can't be of much help...
-Rob
Scott Harrington <sharrington@xxxxxxxxxxxx> wrote:
Hello everyone. I am new to this list, so please accept my apology if
this has been covered at some point in the past (I did check archives
though). Also, I hope this is the correct place for this.
I don't even know if my problem is IETD specific, but I'm fresh out of
ideas. I will try to include as much information as possible, while
attempting to keep it relevant. I've been trying to solve this problem
for going on two months now with no luck.
I currently have 4 boxes running Mandrake 10.2 and IETD 0.4.13. Kernel
version is 2.6.15. All the boxes are identical with a Celeron 2.8 and
512MB of RAM. Each box has an 80GB IDE boot drive and 4x300GB SATA
drives configured as a raid 0 under /dev/md0. IETD is configured with
Lun 0 Path=/dev/md0,Type=fileio. These boxes are all connected together
with DLink DGE-530T gigabit NICs to an EG008W gigabit switch (dedicated
to the iSCSI targets and initiator) with no jumbo frame
support.
Incidentally, the motherboards are Intel D915GAGLK boards and the
onboard gigabit NICs don't work reliably with any kernel I have tried.
At the initiator end I have a Windows 2000 box running MS's 2.0 iSCSI
Initiator software. It attaches to each target, and then I have it set
up to software raid 0 the 4 mounted iSCSI targets to make one ~4.3TB
drive. I am aware that there is no redundancy anywhere, but that's ok
for my purpose - I'm using it as a Disk-to-Disk-to-Tape solution. If a
drive fails I know I will have to rebuild the whole thing, but that's
fine with me. The Windows box runs Veritas Backup Exec 9 and backs up to
the "local" D: drive (the mounted ~4.3TB volume). The Windows box is a
P4 3.0 with 2GB of RAM and an Intel dual port gigabit network card.
Now the problem; writes are slow. Very, very slow. This can be simply
copying a file to the drive, or using Backup Exec to backup to the
drive. To give an
example, a 407GB backup I just finished running
completed with an average speed of 204MB per minute. The verify
(reading) finished with an average speed of 2,571MB per minute.
Duplicating the data to tape now is streaming through at ~350MB per
minute which is pretty much the maximum write speed to each tape drive.
The 407GB of data came from a 2Gb/s fiber channel array connected to the
Initiator box via gigabit, but the same problem is observed when trying
to copy data from the local C: drive on the Initiator box to the mounted
iSCSI volume.
To try and exclude the Linux raid as being the source of the problem, I
created a 20GB file on the IDE boot drive of one of the iSCSI target
machines. I then set it up as a target and mounted it on the Windows
box. Unfortunately I noticed the same write performance problems. I
have tried a variety of configuration changes, none of which have made
any difference at all. If there is more info you
want, I'd be happy to
provide it. If anyone could possibly provide any help I would be very
grateful. I think it is maybe cache related as copies / backups usually
start to go very quickly, but then taper off to very slow after about 10
seconds or so.
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