Slow backup - odd problem

[George_Dodds]

I backup using fbackup from sam to a remote dlt 80 drive. Both systems are L2000 running 11.0.

The backup gets to around 10000 lines fine and then slows right down every time.

This happens no matter what time it is run, so it cannot be down to network congestion.

Any ideas?

Cheers

George

[Chris Wilshaw]

Are you using a config file with fbackup to increase the value of blocksperrecord?

The default values with fbackup can be a little slow (as they were defined when fast drives were not available).

[George_Dodds]

No there is no config file.

But the issue is that it was working fine, there have been no changes to the system which is the odd thing.

[Steve Steel]

Hi


Are you on the latest patch level on both machines.

Do any errors occur in fbackup or syslog on either machine

How do you run the fbackup . Command string

What config file do you use
.
Increasing blocks per record can help

-c config config is the name of the configuration file, and cancontain values for the following parameters:

o Number of 1024-byte blocks per record,
o Number of records of shared memory to allocate,
o Number of records between checkpoints,
o Number of file-reader processes,
o Maximum number of times fbackup is to retry an active file,
o Maximum number of bytes of media to use while retrying the backup of an active file,
o Maximum number of times a magnetic tape volume can be used,
o Name of a file to be executed when a volume change occurs. This file must exist and be executable.
o Name of a file to be executed when a fatal error occurs. This file must exist and be executable.
o The number of files between the Fast Search Marks on DDS-format tapes. The cost of these marks are negligible in terms of space on the DDS-format tape. Not all DDS-format devices support fast search marks.

Steve steel

[Steve Steel]

Hi


You have no config file then you have default values .

Change blocksperrecord
Fast search marks
Number of retries to 3


Steve Steel

[George_Dodds]

There are no fbackup errors, i run fbackup from sam - backup files interactively.

Ta

George

[Jean-Louis Phelix]

Hi,

Perhaps your problem could be related to source data f you really haven't changed anything compared to when it was working correctly. Perhaps you source FS has became more fragmented ou you have changed your LVM design.

Regards.

[Steve Steel]

Hi

Tune it anyway

try tuning the number of retries and the amount of medium used during a retry to get more on your tape see below.
Also the reader processes and blocks per record can be increased


Fbackup man page

+ Create a suitable configuration file called config in the directory
/var/adm/fbackupfiles call with -c in fbackup.

Options
-c config config is the name of the configuration file, and can contain values for the following parameters:

o Number of 1024-byte blocks per record.
o Number of records of shared memory to allocate.
o Number of records between checkpoints. Since the EOF marks between checkpoints are also used for fast searching on DLT-format drives, changing the checkpoint frequency may also affect selective recovery speed (see WARNINGS section).
o Number of file-reader processes.
o Maximum number of times fbackup is to retry an active file.
o Maximum number of bytes of media to use while retrying the backup of an active file.
o Maximum number of times a magnetic tape volume can be used.
o Name of a file to be executed when a volume change occurs. This file must exist and be executable.
o Name of a file to be executed when a fatal error occurs. This file must exist and be executable.
o The number of files between the fast search marks on DDS-format tapes. The cost of these marks are negligible in terms of space on the DDS-format tape. Not all DDS-format devices support fast search marks.

Each entry in the configuration file consists of one line of text in the following format: identifier, white space, argument. In the following sample configuration file, the number of blocks per record is set to 16; the
number of shared memory records is set to 16; the checkpoint frequency is set to 256; the number of file reader processes is set to 2; the maximum number of retries of an active file is set to 5; the maximum retry space for active files is set to 5,000,000 bytes;the maximum number of times a magnetic tape volume can be used is set to 100; the file to be executed at volume change time is /var/adm/fbackupfiles/chgvol; the file to be executed when a fatal error occurs is
/var/adm/fbackupfiles/error; and the number of files between fast search marks on DDS-format drives is setto 200.

blocksperrecord 16
records 16
checkpointfreq 256
readerprocesses 2 (maximum of 6)
maxretries 5
retrylimit 5000000
maxvoluses 100
chgvol /var/adm/fbackupfiles/chgvol
error /var/adm/fbackupfiles/error
filesperfsm 200

Each value listed is also the default value, except
chgvol and error, which default to null values.


steve Steel

[John Palmer]

Could it be that at this point, fbackup encounters files that are compressed and consequently much slower to backup. Akternatively, are you backing up NFS mounts?

I'd check with glance what files fbackup has open when this occurs.

Regards,
John

[Robert Thorneycroft]

It might be worth just checking exactly which files are being backed up at this point as it is quite likely that the cause of the slow backup could be attributed to a large amount of small files.

The reason for this is that DLTs like a constant stream of data to be provided to keep the media constantly moving, if for any reason this does not occur the tapes will begin stopping and starting which has a very detrimental effect to the overall backup time.

I used to experience similar problems and found that the following conf file now works pretty well.

blocksperrecord 128
records 64
checkpointfreq 512
readerprocesses 2
filesperfsm 1000

[George_Dodds]

Only backing up local filesystems, will check on files it slows down on.