On Fri, Sep 19, 2008 at 02:51:03PM -0400, John Stoffel wrote:
A> On Fri, Sep 19, 2008 at 12:57:25PM -0400, Bill Holland wrote: A> Yeah. Tape motion works fine. I just wanted to see if I could A> direct OnTap to read the tape rather than deal with netbackup.
Did you enable DAR with your NDMP backups? As I understand it, DAR allows the backup software to move the tape to the closest position near the file to be restored, which makes things much faster. Otherwise it needs to scan the tape sequentially...
Correct. Or at least what I've done is to not disable it. My restoration log says that DAR is enabled, but it still took a couple of days to restore.
A> While netbackup/NDMP is restoring the file, I see very slow reads A> on sysstat, but I don't know if that's an NDMP issue or a tape read A> issue.
Hmmm.... does NetBackup use a really small block size?
It shouldn't, but that's why I want to try a 'dd' or similar to see how the tape performs. Other than 'restore', I can't see anything I can do in OnTAP to read the tape.
Maybe NDMP copy could be used to try and pull the backup off tape and send it to another node where you can extract it via pipe to tar (or whatever NetBackups uses for it's internal format) that way?
I'm not sure how I'd do that. The data on tape is wrapped in a netbackup header, so I don't think OnTAP will like looking at the data.
A> I can't get near that on the LTO-3. I never get faster than A> 80MB/s. The restore is around 100 KB/s.
That's just way too slow. I assume it's a fibre channel drive? All the way down to the drive? You'd think even a plain read/scan of the tape would fly.
Correct. Just a straight path from the controller to the drive. Not even a switch.
What happens if you create your own backup tape(s) on the filer using plain 'dump' commands to the same drive. Can you then read it back more quickly? That will at least give you more confidence that you've got a good connection.
Well, just the fact that the dump runs at good speed makes me think the connection is good. But yes, I suppose I can do a dump/restore test. But I'd rather test this tape... :-)
Speaking of that, maybe you've got a flaky fibre connection or dirty optics? Try re-seating both ends of the cable to make sure you're getting the right connection. I remember one with a 50pin (or was it 68?) where we bent one pin in the connector and it just failed down to old SCSI-1 speeds, but it did work. Just really really slowly...
Backup speeds (80MB/s) are fine.