How to get restore to ignore a CRC errors

[erik_k]

During a volume or file level restore I get "failed to decompress lz4 block" error and the restore is aborted.
I know this is caused by a corruption of the backup data and I know restoring bad data is not a good thing.
Some time ago I learned there is a way to tell Veeam Agent for Windows Restore to ignore the error and continue but I can not find how to do this.
Can someone help me?

[HannesK]

Hello,
and welcome to the forums.

Some time ago I learned there is a way to tell Veeam Agent for Windows Restore to ignore the error

is there maybe a confusion with backup where the agent can ignore corrupted blocks?

From my point of view, the data is lost. Also see discussion here

Best regards,
Hannes

[erik_k]

Hannes,
The backup is located on a zfs mirror that recently has been checked. There where no checksum errors. In file restore mode it is possible to restore from the backup. Some files can not be restored. But when the restore hits a bad block (?) and asks if it should continue the break file level mount disappears and the continue fails.
Question: Why is file restore so slow? It seems to take at least 40 hours to restore 400GB?
What can I do to speed up file level restore?
All my full backups seem to have errors. Is there a utility that can check a backup?

[HannesK]

Hello,
as you say zfs mirror, I guess the data is stored on a consumer NAS system. These systems are known as number one reason for data loss. That is because of poor SMB protocol implementations of these vendors.

With health check enabled for today, there should also be errors then.

The speed of file level restore depends on the hardware and how many files you restore. Millions of small files are slower than a few large files. The easiest way to test is doing "copy & paste" with the same type of files between the same types of hardware (e.g. 50k files with total amount of 4GB between the agent computer and the backup device).

Best regards,
Hannes

[erik_k]

Hannes, thanks for the quick and clear answers.
The nas runs FreeBSD which I assumed to have a very good SMB implementation. After restoring the windows PC the health check hopefully will warn on future corruption.
I am using file level backup as an insurance against ransomware. Is there any space advantage in volume level backup?

[HannesK]

that sounds like Samba for the SMB implementation... same like the NAS boxes I mentioned earlier.

It depends. If you only back up a few files, then file-based-backup is using less space than volume backup. Volume (block-based) backup only needs to back up changed blocks of a file. If for example a 10GB Outlook PST file has a change of 1MB, then file-based backup needs to back up 10GB. Volume-based backup is only backing up 1MB (I simplified a bit, but that's the concept).