Don,
How are your disks laid out is all the data in one large aggregate?
What type of data do you have on your system? Lots of small files, fewer larger files? Very compressible files?
The Phase 1 scanning of files has a significant impact on filer CPU whilst it is performing this. If you have a lot of small files then this process can take along time to complete. If Phase 1 is taking a significant amount of time to perform then running 2 together will extend the backups.
When you run one backup check the output of a sysstat to see what rate the data is being written to tape at.
LTO 3 runs at 80MB/sec native and upto 160MB/sec with compressible data. A 2GB FC runs at 200MB/sec, 2 tape drives on one FC loop will potentially start to slow each other down with compressible data.
If you backup window is too small then you have to start looking at ways to decrease the amount of data you are backing up each night. Do you have to do full backups of every volume every night? Why not rotate the volumes you are doing full backups of around the week and then just do incrementals of the other volumes every night. Or perform full backups at a weekend and then incrementals every other night.
-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Glascock, Donald Sent: 10 October 2006 21:24 To: toasters@mathworks.com Subject: FAS960: backup speed vs simultaneous dumps...?
Hi, Toaster folks --
We're a small research group on our third Filer, which is a single FAS960 with five shelves on two cross-connected 2-Gb loops. We trigger flexVolume-level dumps of our one aggregate directly to 2-Gb-fibre-connected LTO-3 drives.
When we dump two volumes simultaneously to two tape drives, the time taken to dump each volume increases by a third to a half again, compared to dumping each volume independently. For example, a stand-alone dump may take two hours, but if another dump of another volume to another drive is run simultaneously, then that two-hour dump becomes a three-hour dump. Adding a third simultaneous dump to a third drive causes an even greater increase in dump times.
For diagnostic purposes, I've launched a conventional dump of one volume triggered via NDMP our backup software, waited for the dump to reach Phase-IV (the writing-data phase), and launched from the FAS960's console a dump of another volume to the FAS960's null device. Soon after this second dump starts, the write speed on the tape drive associated with the first dump falls off by quite a bit. This write speed picks up instantly when I kill the second dump. Since the second dump was only in Phase-I (inspecting files, but not writing them), and since this second dump was to the local null device anyway, I'm led to think that the performance issues lie somewhere within the Filer's head and Disk I/O subsystem.
With one-at-a-time backups of our volumes, our full backup window is about eight hours (for about two terabytes). We were planning to buy two more shelves in early 2007.
Should I expect a FAS960 to handle two or three simultaneous full dumps without a significant loss in dump speed? Are you getting nearly-linear performance out of your simultaneous dumps?
Thanks for your time & have a great day!
Don Glascock