Re:I wound up causing a major outage of my services and dest...
by db48x on Friday February 18, 2022 @04:27PM
(#30391335)
> The command told it to reattach the drive and they expected it to rebuild but instead md saw part of the mirror and simply added the drive as a good drive.
> ZFS catches these tricks because the checksums will fail.
Yea, I think this is the right explanation. I guess it simply doesn’t keep any consistency information that it can check, whereas ZFS keeps a checksum of every block. Having used ZFS, it is difficult for me to understand how anyone could trust anything else. I don’t think that there is anything a ZFS user could do to accidentally destroy their data (aside from obvious things such as deleting the wrong filesystem or pool, which could happen in any case).
And the drive would return bad data instead of just erroring out - this is sometimes a difference between “home use” drives vs enterprise - enterprise assume you’re in a multi redundant raid setup and instead of retrying will just fail out fast and let the raid take care of it. Home drives will continue retrying and perhaps even eventually give you what they got - the idea being you’d rather have one byte bad of a word doc than lose a 4K chunk of it.
ZFS catches these tricks because the checksums will fail. Multi-redundancy RAID can do it - but since most are enterprise they are built with the assumption the drive will return good data - or none.
This can be the worst scenario as corruption can be silent and infect all backups after a time.