Hello and thanks in advance for reading,

We've been having serious read performance issues with Open-iSCSI.

I'll list the specs of our setup first:

The SAN:

- Dual-Core Xeon with 2GB RAM, running Microsoft Windows Storage
Server 2003 R2
- 5TB storage, sliced into two 1.5TB and one 2.0TB partition.
- Dual Broadcom NC324i NICs
- 1Gbit uplink to switch, using the first Broadcom card.

The client machine experiencing the problem:

- Quad-Core Opteron with 8GB, running Gentoo Linux, kernel 2.6.24-
gentoo-r5
- It uses the 2TB iSCSI Target, formatted as xfs and used as backup/
restore for local storage
- Dual Broadcom BCM5708 NICs
- Intel 82545GM fibre NIC
- Open-ISCSI version 2.0-870-rc1 (latest version)
- 1Gbit uplink to switch, using the Intel NIC (fibre).

The switch:

- Cisco 3750G, 24xCopper Gigabit switch with three fibre-modules

The problem we're experiencing is this:

When we copy a file from the local disk array to the iSCSI target, the
write performance is amazing: we max out the gigabit link immediately
(>100MB/sec writes easily). When we copy a file from the iSCSI target
to the local disk array however, performance is absolutely *dreadful*:
1-4MB/sec. This also completely floods the client machine with I/O
requests (as seen by running 'htop'): the load jumps to ~6-8 and it
becomes very slow and almost unresponsive to commands.

What I've tried to rectify the problem, is what I could find online so
far:

- Enable Flow Control on the NICs: no change in speed.
- Change to the copper NIC on the client machine: no change in speed.
- Use different read-ahead settings on the SCSI device 'blockdev --
setra ...' (4096-65536). This only initially solves the problem: we
get a short burst of good speed, and then it dies again. It kills the
random reads/write speeds, however.
- Different programs make no difference: the problem occurs with bonnie
++, cp, scp, mv, etc.

Can anyone help me figure this out, or point me in the right direction?
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