Fbackup and Ultrium 460

[Douglass Anderson]

When I use fbackup (default settings for -c ) to my Ultrium 460, I get 18 MB/Sec (66 GB/Hr) not the 60 MB/sec (216 GB/hr). I have all the patches (PHCO_31314).

How can I increase the backup speed?

I have tried a few -c settings listed in other forum answers, but it does not change much.

thank you.

[James R. Ferguson · Accepted solution]

Hi Douglass:

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 decent performance with modern tapes and tape drives. A much better set of parameters looks something like this:

blocksperrecord 512
records 64
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 a 'frecover' session too.

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, however, FSM's improve the time it take 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!

[Bill Hassell]

18 Mb/sec is the slowest the tape can go with DRM (Data Rate Matching). When the tape is this slow, the data is not arriving fast enough. As James points out, you need to configure fbackup to handle a very high speed device. Now if this does not improve the backup speed significantly, then your system is too slow for this product. 60Mb/sec is an enormous speed, especially if there are thousands of files to backup. That's why fbackup can start up to 6 parallel reader processes to keep the shared memory buffer full and the tape drive busy.

So the first check is for the disks--what is the native long-term transfer speed? Disk arrays can bufer immense amounts of data but eventually the buffers are full and now the transfer slows to the actual speed of the disks.

The next check is for the quantity of files. 100Gb in 5 files will MUCH faster than 100Gb in 5000 files. And if the system is busy, fbackup will be competing with all the other programs to read the files.

Another issue is compressability. Since most of the device files are BEST density (meaning hardware compression is on), if the files can be heavily compressed, then the apparent tape speed will be much faster because redundant patterns are reduced to small codes. All the data must be sent over the I/O channel as it is compressed inside the drive.

Now for some marketing disclaimers...60 Mb/sec is *ONLY* possible if all the data is compressible 2:1 or more. Since you have no way to control this, you must assume that only 30Mb/s is possible with random pattern files (like programs and long lists of random data). So 100Gb/hr is about all you can expect *IF* your system is fast enough. Anything more means that you have compressible data.

And the last check is the speed of the computer. It will impossible to obtain even 25Mb/sec on a K-class computer. You need at least 500 Mhz processors (note: 4 or more) and disks with a native transfer rate (disk plus I/O card) more than 30Mb/sec.

The Ultrium 460 (and especially the Ultrium 960) are not just bigger capacity, they are ultra high speed devices that require a very fast system to come close to their maximum speeds.

[Douglass Anderson]

hw limitation