[livinginfear]

I don't use Apple's products. I've never used Time Machine. I have a Synology NAS though. My understanding based upon reading the article, an the comments here, is that Apple's proprietary Time Machine format is to blame here for this corruption. Can anyone here shed some light on the exact cause for this, and whether this is of any concern to a non-Apple user using a Synology NAS?

[vetinari]

My first though was, that there must be something wrong with the cables, and occasionally a packet is damaged. And at the end of the article, there it goes, powerline.

If you are using unreliable connection, use something that can verify the transfer, rsync, for example.

[MonaroVXR]

Not sure if that's the issue

[vetinari]

Either that, or bad RAM, and the copy buffer hit it.

In the pictures, it seems too regular.

[pfranz]

> My understanding based upon reading the article, an the comments here, is that Apple's proprietary Time Machine format is to blame here for this corruption.

How did you get that? From reading the article it sounded like they just moved their RAW files to the NAS (no Time Machine involved). One thing they use for backup is Time Machine, the RAW files came from a USB drive that they had wiped, but they forgot to attach it during any backup so they were omitted from the Time Machine backup. The details were light in the post so I'm inferring most of this. I'm not sure how "Apple's proprietary Time Machine format" (it's a disk image and the actual data is just files) were to blame.

Time Machine on a NAS (unrelated to Synology) can have problems. macOS generally tells you "verification" failed and recommends starting a new backup...which sucks, is time consuming, and you're at risk of data loss during the initial backup, but is way better than keeping around a corrupt backup. I've used a Time Machine network backup as one form of backup for many many years; both hand rolled and on a Synology. The times I get a corrupted backup I've: manually mounted the backup disk image while a backup started or I disconnected or closed my laptop while backing up. I'm not sure if the problem is on Apple's end or on the server's implementation of Time Machine or the SMB or AFP implementation. I've generally been able to "repair" these backups by running disk utility (fsck) and changing the value in a config file, but that can take a very long time over a network and I'm not sure I'd trust that backup anyway.

I think the cause of the problem was close to what the author suspects. Something got corrupt in reading, transferring, or writing the data. Maybe it was non-ECC ram, bits flipped in transit (due to hardware or protocol), or a corrupt disk. The source data seemed ok since he could recover it, the disks appear ok since they wrote ok a second time--but maybe it wrote to a different area of the disk? I've had RAM issues that only showed up under certain circumstances. Maybe "Enable data checksum for advanced data integrity" was on the second time? I kind of think confirming data was written correctly and using a filesystem that protects against bitrot (or keeping hashes of the files yourself) are the most accessible ways to prevent this. Unfortunately, knowing the hashes no longer match means you just know the files are corrupt and won't help you unless you have another copy.