When the option 'Allocate the maximum size for backup-to-disk files' is enabled, the creation of Backup-to-disk files is extremely slow.
I have observed delays of up to 15 minutes for a 4GB file!!! (= 266MB/min = 35Mbps).
The use of
Process Monitor shows me that it actually uses the full 15 minutes to create the file. It repeatedly writes 65KB (empty?) blocks.
Jobs remain in a state of 'Loading Media' while the file is being created, and thus the overall throughput decreases, and the total run-time of all jobs is too high.
For a server with +/-100GB of data, this adds an unwanted delay of +/- 4 hours, on top of the time which is actually needed to transfer the data over the network.
I know there are several kb-articles that recommend to turn this feature off, but would like to use it, in order to prevent unneeded file fragmentation.
I didn't measure the maximum speed of the disk subsystem, because the
creation of an empty file of 4GB should be MUCH MUCH faster than 35Mbps.
I have done file copies over the network, which achieve sustained throughputs of over 500Mbps to the same target disk!
Even BackupExec itself (other routine) is able to write at a speed of +2000MB/min (= 267Mbps), which is about 10% faster than the observed file-creation-speed, and probably even faster!
By using
CONTIG or CREATFIL (part of the
Server 2003 Resource Kit) it is possible to create a file of any given length within milliseconds.
When you capture the disk I/O by using 'Process Monitor', you can easily see the difference between the file-creation routine of CONTIG versus the B2D-file-creation-routine of Backup-Exec.
I even tried to pre-create the BKF files using CONTIG and import those into BackupExec, but with no luck :(
Most likely the 'empty' BKF will have some kind of header which need to be created, but I guess it's only a minor change to first create an empty file, and then overwrite the first few kilobytes to set the appropriate file-header.
Kind regards,
Br_nar
P.S.: I use Backup Exec 12.5 SP3 + latest hotfixes installed
