Hi,
We're noticing that when copying a large file (3gigs) to a volume that is housed on a SATA aggr, that latency is signifcantly increased on another SAS/SCSI aggr in the same filer. Is this considered normal behavior?
When I say latency, there are a couple of things which give this away:
1) We run Oracle on our SAS volumes/aggr's, and the Oracle logwriter begins alerting for latency when we copy large files to the SATA aggr.
2) Using 'dd' to write a small 1kb file test every 1second, we notice increased latency (from less than 1ms to 10seconds) during the file copy
3) We see 'nfs not responding' messages on systems which are mounting SATA volumes over UDP:
Such as:
Aug 29 01:04:31 xxx kernel: nfs: server 10.0.255.24 not responding, still trying
Aug 29 01:04:31 xxx kernel: nfs: server 10.0.255.24 OK
Aug 29 01:05:53 xxx kernel: nfs: server 10.0.255.24 not responding, still trying
Aug 29 01:05:54 xxx kernel: nfs: server 10.0.255.24 OK
We only stumbled across this due to issues experienced by some of our Oracle databases, we had systems on SATA aggr's which were generating high I/O and thus causing latency on one of our SAS aggr's. We also find that the latency is experienced towards the end of the file copy, which makes us wonder if we're hitting some kind of backlog of I/O on the filer?
thanks in advance