How does rsync file verification work?

[Kevin Korb]

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Rsync does not verify the data after it is written to the disk.  The
whole file checksum is only done to ensure that the file crossed the
network intact.

This is not unusual.  Backup programs generally don't re-read from the
target to confirm a successful write.  In fact if they did they would
probably just be reading from the cache anyway.

If you are really paranoid about this then you need a separate file
verification tool.  Plus you need to make sure the cache is dumped
between the rsync run and the file verification run.

Note that the only time I have seen rsync write corrupt files was when
a bad DIMM was corrupting data in the cache.  The solution to that is
ECC RAM.  The only other way I have heard of it happening is a failing
disk in the backup system and the solution to that is SMART monitoring.

On 02/04/12 11:54, Moqi Ba wrote:
> Hello,
> 
> I want to use rsync to create backups. I think I need a
> verification that: 1) data is written to disk. 2) data is read back
> from disk. 3) verify the checksum of data. Does the automatic file
> verification in rsync works like this? Technically, I'd like to
> know how does we make step 2 read data from disk and not from file
> cache/buffer in OS? Or, do OS/harddrives always perform written
> data verification anyway so step 2 is not really needed?
> 
> Thank you. Moqi Ba
> 
> 

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	Kevin Korb			Phone:    (407) 252-6853
	Systems Administrator		Internet:
	FutureQuest, Inc.		Kevin at FutureQuest.net  (work)
	Orlando, Florida		kmk at sanitarium.net (personal)
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