Backup Takes Longer At Month End Than Begining

sql 2005 stnd on a server of decent spec.

dbase in question is only about 5GB on a 450GB partition.

at the begining of the month I run:

BACKUP LOG [objectstore] TO DISK ='D:BackupsProdackup_objectstore.BAK'
WITH NOFORMAT , INIT , NAME = N'objectstore backup'

and then every 10 minutes (within working hours) for the rest of the month I
run:

BACKUP LOG [objectstore] TO DISK ='D:BackupsProdackup_objectstore.BAK'
WITH NOFORMAT , NOINIT , NAME = N'objectstore backup'.


The amount of data that gets backed up is the same through out the month and
the loading on the server as a whole also stays constant throughout the month
- NOTHING increases throughout the month that would affect this server in any
way, yet at the begining of the month the backup takes 10 seconds, and at the
end, it gets up to 5-6 minutes.


why?


THanks

Alastair Jones.


"A computer once beat me at chess - but it was no match for me at kick boxing" - Emo Phillips.