Peoples,

I recently set up our new NDMP backup system (new ADIC Scalar-1000 tape library, with 2 F760s acting as NDMP hosts with 4 drives attached to each from the unit).

Initially I was having trouble getting other filers to backup via the network to the remote drives on the 2 hosts. I was running all my filers on a private 100Mbs Full-Duplex network (utilising the filers' e0 interfaces or quad cards). Funny thing was, I keep seeing really slow and spotty xfer rates and tape writes: small bursts of 65Kb/s then a few seconds of nothing. When I tried backups via dump to local drives, it was 4-6Mb/s, as expected). So, what was causing the painfully slow performance??

On a whim, knowing I had seen something like this before a long time ago with Legato's client pak s/w, I reset the NDMP hosts' ether interfaces to 100Mbs HALF-duplex. As soon as that duplex setting kicked in, my network xfer rates and tape write shot up to the expected 4-6Mb/s rates.

Now, I understand that duplex settings can affect network performance, and that in backups I'm essentially streaming data in one direction (which would make half-duplex a sensible option), but as for WHY I needed to set to half-duplex is a mystery. I would think being Full-duplex would be just as well.

This duplex issue is, as far as I could tell reading over Netapp and Veritas docs, not address explicity when talking about 3-way backups.

While I'm glad I seem to have fixed the problem, the fact that it was a problem puzzles me.

So for anyone out there doing 3-way backups or dumps to remote tape drives, had you seen this before? Is anyone running NDMP and remote drives but not using half-duplex network settings?

Just curious.

-Scott Mikusko