We backup a 1TB VMWare File Server using VMWares VCB with Symantec Backup Exec 12.0, everything is connected with 4Gb fibre
Over the last few months our job rate has slowly dropped from around 1600Mb/s to a disappointing 650Mb/s.
For some reason after tring everything imaginable the problem was solved by simply defragmenting the drive being backed up.
I finally tried this after finding a similar story on vmware forum
I just did some tests with BackupExec 12 and file level vcb over san (not FullVM).
My environment is a LTO4-Library and a 2Gbit FC-SAN-Connection.
I backed up 2 drive letters (C:\mnt\machine\letters\c and c:\mnt\machine\letters\d)
C: contains a defragged plain windows 2003 installation and nothing more.
D: contains 3,5 GB of userdata that I have copied over from a fileserver.
Now the interesting part:
Backup speed for C: -> 850 MB/min
Backup speed for D: -> 3500 MB/min (!!!)
I tested this multiple times, so this is reproducable.
I conclude from this the following:
The speed seems to be affected by the structure/linearness the data is layed out on the disk.
Even that C: is fully defragged (using the build in windows defragmenter), the speed is not that great.
BackupExec just backs up linearly the directory structure, but the files on C: are not laid out that way and the internal Window defrag does not sort by dir/file.
D: on the other hand has a fresh structure, that has been copied over using the normal windows explorer. This structure is completely clean as all dirs and files have been copied over “sorted”.
This is the only explanation for me that the backup speeds are so different.
The observation is furthermore proven by the following:
I ran “jkdefrag.exe -a 7 c:” and the backupspeed of C: jumped from 850 MB/min to 2200 MB/min (!!)
The option “-a 7” sorts the defrag by dirs/files.
JKdefrag can be found at http://kessels.com/JkDefrag/index.html
The program is not suitable for very large file servers, so use with caution!
So, if you have any issues with VCB speed, just try to give the problem vm a new disk (e.g. 10 gb) and copy a bigger directory structure to it. Then do your benchmarks.
Hope this sheds some light into the whole topic here. “
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