Can anyone recommend a best practice for the following scenario?
We currently have a 3750 stack of 9 switches to which all our servers are connected. We have created a vlan (vlan 12 not routed) that we use to connect all the servers that we wish to backup. Lately the server team has seen a drop in backup speed. When we first deployed the stacked switches the backup speed was very slow so TAC support had me apply the following:
mls qos queue-set output 1 threshold 2 3200 3200 100 3200
mls qos queue-set output 1 threshold 3 3200 3200 100 3200
mls qos queue-set output 2 threshold 2 3200 3200 100 3200
mls qos queue-set output 2 threshold 3 3200 3200 100 3200
That change worked wonders for the speed issue but now there is slowness again.
There are no errors on ports and the backups stay within the stacked enviroment. There are no other slowness issues with anything else but the nightly backups.
Are they 3750Gs? If so, do you realize 3750Gs are not especially high performance switches especially in a maximum stack? Too many concurrent host backups might easily overwhelm the stack ring capacity. (The 32 Gb ring is dual 8 Gb duplex, which, I believe, copies each member switch's packet to every other switch member. [NB: the 3750-E has 2x bandwidth and is much smarter about what it places on the ring and how long it stays on the ring.])
You might check whether some new backup server hosts haven't been recently added and/or existing backup times don't newly overlap (easy to do if backup volume has been increasing).