[DRBD-user] DRBD (write) Performance on Intel e1000

Rudolph Bott rbott at megabit.net
Tue Dec 16 21:23:39 CET 2008

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


Hi List,

I was wondering if anyone might be able to share some performance information about his/her DRBD setup. Ours comes along with the following Hardware:

Hardware: Xeon QuadCore CPU, 2GB RAM, Intel Mainboard with 2 Onboard e1000 NICs and one additional plugged into a regular PCI slot, 3ware 9650SE (PCI-Express) with 4 S-ATA Disks in a RAID-10 array

Software: Ubuntu Hardy LTS with DRBD 8.0.11 (from the ubuntu repository), Kernel 2.6.24

one NIC acts as "management interface", one as the DRBD Link, one as the heartbeat interface. On top of DRBD runs LVM to allow the creation of volumes (which are in turn exported via iSCSI). Everything seems to run smoothly - but I'm not quite satisfied with the write speed available on the DRBD device (locally, I don't care about the iSCSI part yet).

All tests were done with dd (either copying from /dev/zero or to /dev/null with 1, 2 or 4GB sized files). Reading gives me speeds at around 390MB/sec which is way more than enough - but writing does not exceed 39MB/sec. Direct writes to the raid controller (without DRBD) are at around 95MB/sec which is still below the limit of Gig-Ethernet. I spent the whole day tweaking various aspects (Block-Device tuning, TCP-offload-settings, DRBD net-settings etc.) and managed to raise the write speed from initially 25MB/sec to 39MB/sec that way.

Any suggestions what happens to the missing ~60-50MB/sec that the 3ware controller is able to handle? Do you think the PCI bus is "overtasked"? Would it be enough to simply replace the onboard NICs with an additional PCI-Express Card or do you think the limit is elsewhere? (DRBD settings, Options set in the default Distro Kernel etc.). 

Mit freundlichen Grüßen / with kind regards

Rudolph Bott
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