How to speed up restoring a file backed up with sam?

[webber_1]

I installed a HP-UX 11.00 system. I backup all file system with sam into DDS2 tape.

I want to restore the file /etc/hosts. I use sam to restore it, but it cost sereval hours. How to restore the file more quickly?

[Mridul Shrivastava]

u recover it manually using frecover, check man page for more frecover options.

# cd /destination_directory
# frecover -f /dev/rmt/0m -xXov -i /source_directory_or_file

[DCE]

You can use frecover to specify /etc/hosts specfically. (see the man page for specifics.

When you do a restore via SAM you actually are using frecover. You can see the actual command in the samlog.

You can also specify the /etc/hosts as the only file to recover in the sam restore screen. It should restore fairly quckly, unless there is a problwm with the tape drive and/or tape

[Steve Steel]

Hi

Is it a local or a remote tape

The frecover command shown to recover to local directory is ok but if you use a system:/dev/rmt/?? format then it doe snot use the fast search to recover.


Just try it manually and locally.

If tape is on other machine then compare the recover time for an unimportant file between local and remote

Steve Steel

[Steven E. Protter]

Shalom webber,

DDS2 is slow and if the file is near the end of the tape it will take as long as it takes. There is little you can do other than to in the future make smaller discrete backups of more critical files.

Assuming your system is running correctly and the drive is local it takes as long as it takes to read the tape.

SEP

[V. Nyga]

Hi,

I believe, only a newer tape drive will do it faster - I changed from DDS2 to DDS4.

HTH
Volkmar

[James R. Ferguson]

Hi:

If you are not using a 'config' file with 'fbackup' you are going to get very poor backup performance.

As documented in the man pages for 'fbackup' in the absence of an explicit configuration file ('-c config'), default values are provided. However, these defaults are archaic and will not yield good performance with modern tapes and tape drives. A much better set of parameters look something like these:

blocksperrecord 256
records 32
checkpointfreq 1024
readerprocesses 6
maxretries 5
retrylimit 5000000
maxvoluses 200
filesperfsm 2000

These parameters are recorded onto the actual backup tape and are thus used for recovery sessions with 'frecover'.

Checkpoint records allow the salvage of a backup when a bad tape spot is detected, since the records contain information about the file being backed up. The 'filesperfsm' parameter controls the frequency with which Fast Search Marks (FSM) are written. Both checkpoint and FSM records affect performance. FSMs take a tape drive out of streaming mode thereby adding to backup time. Conversely, FSMs improve the time it takes to recover a file from tape.

In general, if your backup consists of a high proportion of small files, increase the value for 'filesperfsm'. If your backup consists of a high proportion of large files, then decrease the 'filesperfsm' value.

Regards!

...JRF...