I have asked this question in the past but never really got the explaination I was looking for. I have struggled with understanding the different types of snapshot methods offered for windows. I have read thru the snapshot admin guide and yes it offers some explainations and excellent instruction on how to setup the backup types but i was hopeing for an explaination that i can understand. :)
I dont really know what the difference is in selecting flash-backup for windows and selecting ms-windows with perform snapshots checked. Does one offer better performance or are they essentially doing the same thing? Below is a configuration for some of my servers and maybe if someone can explain which type of backup would be prefered for each i might graps the concept a little better.
I have a couple of policies with type ms-windows and the perform snapshot backups selected. The method is left at auto. Netbackup version 7.1
I know there might not be much hope for the imaging systems but i atleast want to make sure i am using the best method possible to backup the data.
With a classic backup, for each file, there are system calls to open/read/close it. It's an important overhead of your backup process when you've got partitions with loads of small files. In this case, flash-backup is meaningfull because the partition is read in block mode. IO rate is dramatically improved. Thanks to the map facility, you can still restore individual files. In case of a restore of the whole partition, restoring in raw mode gives best results (as i've recently experienced :)
The counter-part you have to keep in mind for flash-backup : the entire partition is backup, whatever its capacity rate.
So what your saying is with flash-backup you have to backup the entire partition. I cant pick an individual folder on that partition and use the flash-backup feature?
Also what is the purpose of the snapshot feature for an ms-windows backup. Is this not the same thing?
If you choose "windows flash-backup" to backup, let say "Y" partition, the syntax is in the policy definition is "\\.\Y" and the whole partition is concerned. Partition is read in raw mode, block by block. The driectory and file structure is defined in upward layer (NTFS). You can't get rid of the upward layer to speed up your backup and in the same time use if to pick only some parts. Life's always a matter of choice and compromise :)
The snapshot feature fo ms_windows backup is a buffer used to hold modifications while backing up opened files. So it's a facility to garantee the consistency of an opend file, not to speed up backup.