Poor write performance when replication is on

[juelz]

Hello,

I've set up a replication between two DSS servers.

When I start the replication process, it synchronizes both volumes and reports "Consistent" on each volume. I start copying files then (or dd'ing some data) to the iSCSI volume, but this is really slow (dd reports 5-10 mb/s). When I turn off the replication, the write throughput is from 80 to 100 mb/s (which i quite good for a 1 gbit/s network).

Both servers are linked directly to each other using a cat 6 patchcable (crossover is not needed, because both NIC's support Auto-MDI-X). drbd initially synchronizes the volumes also with 80 to 100 mb/s speed.

What could be the bottleneck, when replication is turned on?

Thanks!

[To-L]

Please set a higher value for the parameter VMALLOC. This
can be done via the console tools (CTRL+ALT+W > Tuning Options > Vmalloc
size).
Are you connecting to the destination directly, and you are connecting to the source from another NIC.

[juelz]

Hi,

I increased vmalloc to 384mb on both servers, but the problems still exists.

2097152000 bytes (2.1 GB) copied, 473.446 s, 4.4 MB/s

Both servers are connected directly through crossover cable (eth3 on both, 1 gbit/s). The iSCSI initiators are accessing the source through eth4 & 5 (bonded, 2 gbit/s).

Any ideas?

[To-M]

What is the version of DSS you are running?

[juelz]

Version:                        5.0.DB47000000.3216
Release date:                   2008-08-28

[To-L]

Please upgrade to the latest version of DSS
Here is the link:
http://www.open-e.com/account/products-and-updates/

[hugor99]

I am experiencing the exact same thing. Turning replication on drops my write speeds to 10MB/s maximum and only slightly reduces my read speeds. With it off I can get close to 112/115 MB/s in IOMeter reading and writing.

I have DSS V6 6.0up13.810.3902 64bit. I cannot change the VMALLOC setting as it is 64 bit. I am no keen on updating, as VMWare only has 3902 on their HCL for Open-E, and I want to be able to get support from them if needed.

Any other suggestions?

[To-M]

You wont be able to change this in 64bit mode - there is a new release coming out this Friday and we did some more tuning on this subject, also the 3902 is using the same SCST Target solution so it is ok to update.

[hugor99]

You wont be able to change this in 64bit mode - there is a new release coming out this Friday and we did some more tuning on this subject, also the 3902 is using the same SCST Target solution so it is ok to update.

So I upgraded to 4221 and I'm still getting 12MB/s max replication during the initial synch, even though I set the speed to 60MB/s.

Any other suggestions?

[To-M]

When I wrote to you in the last message i really meant to say that we will have a new release with some script modification to the replications it is out now for download build 4362.

Is the destination server the same system or slower (RAID array, cpu....)? Also try setting the replication bandwith to 25MB and test if you are getting the same speeds with this setting and the new version then send in the logs to pre-sales@open-e.com (please use the user portal if you have a registered product as this will help you faster) and we will take a look at them.