LVD - DLT 2/20 Tape Library varies on speed of backup

[Bryan Purtell]

We have a LVD - DLT 2/20 tape library that varies from day to day on the speed of the backup. We are using Backup Exec v8.6 running on an LH3000 server with Windows NT SP6a installed. The tape library has 2 DLT drives and is up to date with the firmware. We use Adaptec 2940 SCSI cards.
The largest job is 50gigs and runs over a 100 MB Ethernet connection. The remote server is also running NT, sp6a. It runs with Backup Exec v8.6 and OFO is installed.
There doesn't seem to be any consistency between long jobs and regular jobs. Has anyone else experienced this?

[Vincent Fleming]

I would look at the network first... what's the load like on the network? Is it very consistant, or is there some traffic that could be interfering with the backup data (such as ftp traffic during the backup)?

I think it's much less likely that Windoze, the hardware, or Veritas is causing intermittant slowdowns, so the network is the most likely cause of your problem.

Good luck!

[Michael Tully]

Hi,

I agree with Vincent. Sharing any type of network with a streaming tape with nearly always affect the data going to your drives. There is not much you do can other than to spend money on a seperate backups network, or further equipment to isolate the stream of data.

~Michael~

[David Ruska]

> We have a LVD - DLT 2/20 tape library ...

> The tape library has 2 DLT drives and is up to date with the firmware. We use Adaptec 2940 SCSI cards.

I assume you mean 2940UW cards, not the narrow 2940 card.

The 2940UW is a single-ended card, so it is limited in cable length, and limited to ultra (40MB/s) speeds. The DLT8K drives are LVDS drives, although they can't burst over 40MB/s (LTO can burst to 80MB/s).

I'll also assume you're using one card per drive, with perhaps one drive sharing a bus with the library.

As mentioned already, your network is likely to be your bottleneck. However, one factor to check is the block size. Newer DLT8K firmware seems more sensitive to small block sizes. Use 32k or 64k. See the following for more info:
http://www.hp.com/cposupport/information_storage/support_doc/lpg50167.html

[#5]

May be unrelated but we had similar difficulties. Some jobs would run at 40mb a min thro put and another would run at 450mb min. We eventually traced it to a firmware mismatch, the library had been updated but the drive had not. We upgraded all firmware to the latest rev and all is fine now.

Just thought I'd mention this as we thought it was our network originally but there was never any real load at the time of running the backup.

JJ