I have performed a factory reset my ReadyNAS Pro Pioneer (RNPP) unit. and now want to ensure the restore of the original data from an external USB drive (connected to the NAS' USB port) is copied without any data corruption. I am trying to confirm color=#0000FF]whether RSYNC is a good tool to use to verify the copied data's integrity[/color].I have ready many posts that suggest using RSYNC to verify a backup. One such example:viewtopic.php?f=66&t=51339&p=292769mdgm wrote:...After doing the backup to the USB disk you can verify it using a Rsync backup to USB diskMy questions are:'1) After the initial restore to the RNPP unit (using FrontView's backup job, Source=Share-USBDrive; Target=Share-RNPP Share Drive), I set the backup type to RSYNC.Do I then perform a FULL backup again?2) The expectation is nothing changes during this first RSYNC backup. Question - so, how does RSYNC actually verify the backup? Does it to a byte-for-byte comparison or just a date/time comparison?

You do an incremental backup. It compares the files on the source and destination. If the files are different the changes will be transferred across.Edit: not comparison of checksums, see below.

mdgm wrote:You do an incremental backup. It compares the files on the source and destination. If the files are different (I.e. checksum doesn't match) the changes will be transferred across.First, THANKS SO MUCH for the fast response!!!So, you are saying the (first) RSYNC backup (after the initial full backup/transfer of data) does a checksum verification on each file (source versus target) to determine if two same-named files are different? I am not clear on this because several posts on this forum state that RSYNC uses timestamp/filesize to determine if a file (between source and target) has changed, then if a difference is detected, RSYNC does the delta calculation to determine what delta gets backed up. Here is one such post:viewtopic.php?f=31&t=27318&p=152960ewok wrote:bru wrote:What I want to happen is for rsync to compare dates and checksums of the file andto not backup files that have not changed so that the network does not get hit veryhard and the disks to not get too much usage.That's what rsync does, using timestamp and filesize to check if a file needs to be transferred. Using checksums would be very slow....

Oops. I guess I was wrong then. Using file size and timestamp should be sufficient because one of those is slightly off if the file wasn't copied successfully.

mdgm wrote:Oops. I guess I was wrong then. Using file size and timestamp should be sufficient because one of those is slightly off if the file wasn't copied successfully.LOL, are you sure you are wrong? Again, I have seen BOTH sides of the story. OK, let me ask this. IS there a definitive way to do the checksums verification natively on the NAS? I mean, I can use/run FreeFileSync (http://freefilesync.com/) from my network-connected PC to compare the USB version of the file versus that on the RNPP, but that takes ALONG time because of the time it takes to pull data across my network (100 not 1000Mbps) and my PC is OLD (~4+ yrs laptop), so I prefer not to go that route.

Just had a look and there is an option for rsync to compare (to decide which files have changed) by checksum. From reading your quote of ewok's it sounds like this option is not used by Frontview backup jobs.If you have SSH access you could run rsync manually from the command line with the relevant option specified.

How does RSYNC "verify" integrity of a backup???

mdgm wrote:
... After doing the backup to the USB disk you can verify it using a Rsync backup to USB disk

mdgm wrote:

...

After doing the backup to the USB disk you can verify it using a Rsync backup to USB disk

23 Replies

Replies have been turned off for this discussion

TeknoJnky
Hero
Sep 24, 2011
-c and --checksum are the same thing, see @ viewtopic.php?p=323348#p323348 or google rsync and you will see all the command line options.

winger

Tutor

Sep 24, 2011

TeknoJnky wrote:
I have no way to verify if it did or didn't work, but putting --checksum in the rsync exclusion fields didn't cause any errors and in theory would be passed along to the backup job command line

TeknoJnky wrote:
I have no way to verify if it did or didn't work, but putting --checksum in the rsync exclusion fields didn't cause any errors and in theory would be passed along to the backup job command line

I no files which only differs by a couple of bits, but gave this a test run with a Share that has approx 1.5GB of data (unchanged between source (NAS) and backup target (USB HDD) )

Main difference I see is between the "sent xxxxx bytes" figure
with "--checksum" : 113875
without "checksum" : 113859

Does this tell one way or another if adding the "--checksum" into the "Add files and directories to be excluded as a comma separated list" field (of the backup's Rsync settings) works ?

--------------------------------------------------------------------------------
WITH --CHECKSUM
INCREMENTAL Backup started. Sat Sep 24 10:34:25 PDT 2011

Job: 001
Protocol: rsync
Source: [Datatest]/
Destination: 192.168.0.200::USB_HDD_1/backups/Datatest

sending incremental file list

sent 113875 bytes received 246 bytes 228242.00 bytes/sec
total size is 1529466744 speedup is 13402.15

Backup finished. Sat Sep 24 10:34:25 PDT 2011

--------------------------------------------------------------------------------
WITHOUT --CHECKSUM
INCREMENTAL Backup started. Sat Sep 24 10:33:42 PDT 2011

Job: 001
Protocol: rsync
Source: [Datatest]/
Destination: 192.168.0.200::USB_HDD_1/backups/Datatest

sending incremental file list

sent 113859 bytes received 246 bytes 228210.00 bytes/sec
total size is 1529466744 speedup is 13404.03

Backup finished. Sat Sep 24 10:33:42 PDT 2011

PapaBear1
Apprentice
Sep 26, 2011
Winger - I like many others was basing my comment on apparent incorrect information.

Thank you for opening up this discussion to clarify the situation.

Forum Discussion

How does RSYNC "verify" integrity of a backup???

23 Replies

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