Changing the block size of tape

[malki_3]

Hello everybody

I look for the optimal value of the blocke size that I must assigned to the tape. The target is to reduce the time of night backup.

I have this tape on my server: HP C1537A
Thanks

[Bill Hassell]

The maximum bolcksize is a function of the tape drive,. In this case, the DDS tape drive works well with large blocksizes such as 256Kb. However, tar and cpio don't have the option to change to something like 256Kb, and classic backup tools like tar, cpio, dump, etc are not recommended for full backups due to the many limitations inherent in these old programs.

fbackup will outperform all classic utilities as well as provide high-speed restores of a few files (minutes to get to the end of the tape). Always use a config file with fbackup! If you do not run fbackup with a config file, you will get very inefficient operation for modern DDS, DLT and Ultirum drives (defaults are for reel-to-reel 1/2" tapes). Here is an example of a config file appropriate for newer drives:

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

Put this into a file and then use the -c option. Backup speed is also a function of how slowly the data dribbles out to the tape. If the tape drive is on the same channel as all the disks, it may get starved for data and drop out of streaming mode. This can degrade backup speed from 10:1 to as much as 500:1.