is there a command or option to estimate time and space fbackup will use?

[常有慈悲心]

so i can know how long will the backup will last?

[Fred Ruffet · Accepted solution]

fbackup doesn't compress anything. It adds a little info for restore, so it will save a little more. You can use a 1 for 1 ratio and it will be approx. giving you the space required. (I have here a fbackup saving something like 18GB and stores 101% on tape)

Regards,

Fred

[Geoff Wild]

To estimate time - you could run a test on a few files...

Say for example, you want to backup 900GB of data...

Well, just pick say 90 GB of that data, test it - then multiply the time by 10 as an estimate.

For space, if your tape devices have built in hardware compression, then you may be able to estimate total tape space that way...

Rgds...Geoff

[john korterman]

Hi,
no command available, just a guess, but you have to take a few things into account when making the guess.
The best guess can be made if nothing else is running on your machine. In that case fbackup will probably not need more than a single attempt for copying a file. Else you cannot foresee which files will be in use and how many retries fbackup will make, unless of course maxretries has been set to 0.

But even if nothing else is running on your computer you also need to take into account the number of files and their accumulated size: in my experience fbackup is very fast for backing up a small number of big files, but a large number of files may take a long time, even for a small accumulated size.


regards,
John K.

[Mark Greene_1]

The most significant factor for backup time, assuming backing up to a single tape drive, is being able to keep the tape streaming. If the tape is stopping and restarting a lot because the data isn't being retrieved and sent to the tape fast enough to sustain a continues stream, the latency will kill you.

There are a lot of factors in this including system load, IO contention on the hard drives, sustainable hard drive throughput, sustainable SCSI throughput, and the type of tape drive.

For example, we have identicle L2000s; each does an fbackup of the root volume group every Friday. One system takes 45 minutes to backup, the other 2.5 hours because of the relative load on the system and IO contention on the rootdrives (the samba share is in a VG on the internal drives).


mark

[A. Clay Stephenson]

A much smarter way is to not care how long backups take. One approach (requiring OnlineJFS) is to make snapshot mounts of your filesystems (this takes only seconds per filesystem). Your users can then continue with normal operations and you backup the snapshots at your convenience. When the backup is finished, you unmount the snapshots. Because all the applications are running, you really don't care how long/how fast the backup takes.