[Openstack] [SWIFT] Bad replication performance after adding new drives

Robert van Leeuwen Robert.vanLeeuwen at spilgames.com
Tue Feb 10 11:22:35 UTC 2015

> I set the vfs_cache_pressure to 10 and moved container- and account-server to SSD harddrives.
> The normal performance for object writes and reads are quite ok.

> But why takes moving some partions to only two new harddisks so much time?
> Will it be faster if I add more memory?

My guess: Probably the source disks/servers are slow.
When the inode tree is not in memory it will do a lot of random reads to the disks (for both the inode tree and the actual file).
An rsync of any directory will become slow on the source side ( iirc you can see this in the replicator log)
You should be able to see in e.g. atop if the source or destination disks are the limiting factor.

If the source is the issue it might help to increase the maximum number of simultaneous rsync processes so you have more parallel slow processes ;)
Note that this can have impact on the general speed of the Swift cluster.
More memory will probably help a bit.


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