sam backup to a remote device?

[RobertCarback]

Can sam backup be used to backup to an external network connected remote tape drive such as an LTO?

[A. Clay Stephenson]

Beats me. I can't imagine using SAM to configure a backup that I would trust but SAM uses fbackup and fbackup can be used to connect to a drive on another HP-UX host.

[Bill Hassell · Accepted solution]

Yes, fbackup can talk to a remote tape drive on HP-UX. However, there are a LOT of issues concerning remote backups, not the least of which is the massive performance bottleneck that occurs when using a typical network connection.

The first issue is that remote backup only works with another HP-UX system.

The second issue is data integrity -- there is no error checking between the two systems that the data is an exact copy.

The third is the deal breaker: the LTO tape drive is incompatible with slow networks such as 100 Mbit LANs. That's right: 100 Mbits is VERY SLOW for LTO drives. Remember that a network connection is measured in bits, not bytes, so divide the LAN speed by 10 to get the approximate byte rate with overhead. The divide that number in half for normal performance, or 75% for a really clean LAN connection. So 100 Mbit LAN can see about 5-8 Mbytes/sec performance.

However, the MINIMUM speed for LTO3 drive using adaptive data rate matching is 27 Mbytes/sec, and requires at LEAST 60 Mbytes/sec to run at full speed. Earlier LTO models do not have data rate matching and must have at least 15 to 30 Mbytes/sec to run at full speed. So your LAN speed must be a minimum of 300 Mbits/sec for LTO1 to 1200 Mbits/sec to run the drive at full speed. So you'll need to run at least 4 100 Mbit LAN cards in parallel for slower LTOs, or two GBit cards for LTO3 drives.

Now you might think that full speed is not important, that you just need the data onto another system because this one has no tape drive. But LTO (and DLT and DDS) drives cannot run at slower speeds (one exception is data rate matching LTO3 drives). They work at two speeds: full speed and stopped. If the data cannot arrive fast enough, the drive stops, backs up well into the previously written data, then idles while more data accumulates. Once the tape buffer is full, the drive ramps up to speed, syncs with the old data, then starts writing -- until data starvation occurs again. This stop-backup-restart action is not only hard on the drive and the tape, it slows throughput to 1/50th to 1/100th normal speed.

So the remote tape drive solution carries some very stiff requirements for modern drives. If you can find an HP-UX system with a DDS or even a DLT drive, that should work OK. Oh, the fbackup tape can't be used to restore a dead disk -- you must have a running HP-UX system to read the remote fbackup tape.

[RobertCarback]

Thanks

[RobertCarback]

found solution