Re:Btrfs on Zoned Block Devices
by throw0101a on Thursday April 22, 2021 @07:03AM
(#26901345)
> initial issues
You mean like the current advice not to use anything except mirroring and striping (RAID-0/1/10)?
> Parity may be inconsistent after a crash (the "write hole"). The problem born when after "an unclean shutdown" a disk failure happens. But these are two distinct failures. These together break the BTRFS raid5 redundancy. If you run a scrub process after "an unclean shutdown" (with no disk failure in between) those data which match their checksum can still be read out while the mismatched data are lost forever.
I've been using ZFS since it came out on Solaris 10 over a decade ago and it was specifically designed not to have a write hole due to its COW/ACID nature.
See this 2008 SNIA presentation from Bonwick and Moore, the creators of ZFS talking about not having a write hole:
You mean like the current advice not to use anything except mirroring and striping (RAID-0/1/10)?
> Parity may be inconsistent after a crash (the "write hole"). The problem born when after "an unclean shutdown" a disk failure happens. But these are two distinct failures. These together break the BTRFS raid5 redundancy. If you run a scrub process after "an unclean shutdown" (with no disk failure in between) those data which match their checksum can still be read out while the mismatched data are lost forever.
* https://btrfs.wiki.kernel.org/index.php/RAID56
I've been using ZFS since it came out on Solaris 10 over a decade ago and it was specifically designed not to have a write hole due to its COW/ACID nature.
See this 2008 SNIA presentation from Bonwick and Moore, the creators of ZFS talking about not having a write hole:
* ACID/COW: https://www.youtube.com/watch?v=NRoUC9P1PmA&t=24m
* Integrity: https://www.youtube.com/watch?v=NRoUC9P1PmA&t=55m20s