How does validate REALLY work? If as suspected, it does not seem like a good test.

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According to the manual, archive validation does
"What to validate – select either to validate the entire archive or the latest backup in the archive. Validation of a file backup imitates recovery of all files from the backup to a dummy destination. Validation of a volume backup calculates a checksum for every data block saved in the backup. Validation of the archive will validate all the archive’s backups and may take a long time and a lot of system resources"

This implies the dummy destination needs either enough space to hold the archive to be validated OR they use buffered I/O and test a certain block at a time.

However, it is not obvious what a "validate after backup" does.

I was monitoring all of my Disk I/O using Resource Monitor to see what validate was really doing.

All I saw was a bunch of reads on the tibs, and no writes to disk. It is possible it was doing all of this in-memory, but that is what I came here to find out.

I don't believe I saw it reading the source disks either, which makes me wonder, is validate after backup just reading MD5 checksums inside the TIB file for blocks of data within the TIB file itself?

This is extremely important since knowing how validate really works lets me know if I need to do further testing to ensure data integrity. Any component can have issues or problems and without knowing how it really works, I might be lulled into a false sense of data integrity.

Lun, 02/22/2010 - 13:56
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The validation process doesn't "recover" files for test, it check (in memory, not in disk) the integrity of the data contained into the backup simulating the read done during recovery.

it doesn't compare the files contained into the backup with the files contained into the original disk (also because theese file are surely changed since the beginning of the backup process). if you receive a "success" message on validation task, you are sure that you can restore your backup.

Mar, 03/02/2010 - 16:13
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Hello Carroll and Emanuele!

Thank you for finding time to open the thread and many thanks to Emanuele for highly valuable and correct comment!

I just wanted to add that validation procedure emulates in a way the recovery process on low-level: checks the image sector-by-sector basing on the initial bitmap. This makes this feature rather resource-intensive. The validation of large images (and there is a 1+ TB partition saved within the image) can fail if the system runs out of resources during this process, so make sure that you have enough RAM for it.

There are not strict recommendations regarding the amount of memory required, but if you need to increase RAM, you can find the recommendations here and here. Please keep in mind that RAM is the only resource which is used to process the data during validation. As usual process it surely requires CPU load too.

Should you need anything else or have any further questions - feel free to contact us at your earliest convenience, we will be happy to help you!

Thank you!

Gio, 03/11/2010 - 13:09