In Praise of ZFS on Linux's ZED 'ZFS Event Daemon' • Hacker News Board

Re: In Praise of ZFS on Linux's ZED 'ZFS Event Daemon'

#121

Post by accelbred » Thu, Jul 23, 2020, 6:26 AM UTC

tw04 wrote: post #119

accelbred wrote: post #102

Earlier quoted context omitted.

If you're using RAID-Z on zfs, your comparison isn't fair. Rather than use RAID56 with btrfs, the equivalent would be to get 1 or 2 disk redundancy with raid1 or raid1c3.

RAID-Z is the equivalent of RAID-5. RAID-Z2 is the equivalent of RAID-6. RAID-Z3 would be the equivalent of RAID-7 (or whatever the standard is named for 3-disk parity). This is strictly speaking to how it deals with data and parity, the implementations are obviously different. RAID-1 would be a mirror in ZFS parlance.

BTRFS raid1 isn't mirroring drives though, it means there are two copies of each extent across the whole set of 2+ drives. and BTRFS and raid1c3 and raid1c4 are 3 and 4 copies.

Re: In Praise of ZFS on Linux's ZED 'ZFS Event Daemon'

#122

Post by accelbred » Thu, Jul 23, 2020, 6:28 AM UTC

trasz wrote: post #113

accelbred wrote: post #102

Earlier quoted context omitted.

If you're using RAID-Z on zfs, your comparison isn't fair. Rather than use RAID56 with btrfs, the equivalent would be to get 1 or 2 disk redundancy with raid1 or raid1c3.

Not really - RAIDZ is basically RAID5 without the write hole problem. ZFS equivalent to RAID1 is called 'mirror', and is... well, a mirror.

Yes, and btrfs's raid1 isn't a mirror. Btrfs's raid1c3 and raid1c4 are its alternative to raid5/6 without the write hole.

Re: In Praise of ZFS on Linux's ZED 'ZFS Event Daemon'

#123

Post by [deleted] » Fri, Jul 24, 2020, 9:56 PM UTC

accelbred wrote: post #122

trasz wrote: post #113

Earlier quoted context omitted.

Not really - RAIDZ is basically RAID5 without the write hole problem. ZFS equivalent to RAID1 is called 'mirror', and is... well, a mirror.

Yes, and btrfs's raid1 isn't a mirror. Btrfs's raid1c3 and raid1c4 are its alternative to raid5/6 without the write hole.

[deleted]

Re: In Praise of ZFS on Linux's ZED 'ZFS Event Daemon'

#124

Post by trasz » Fri, Jul 24, 2020, 10:02 PM UTC

accelbred wrote: post #122

trasz wrote: post #113

Earlier quoted context omitted.

Not really - RAIDZ is basically RAID5 without the write hole problem. ZFS equivalent to RAID1 is called 'mirror', and is... well, a mirror.

Yes, and btrfs's raid1 isn't a mirror. Btrfs's raid1c3 and raid1c4 are its alternative to raid5/6 without the write hole.

No, it's still a mirror, just spread over more than two devices. Size overhead is still that of a mirror, ie quite a bit higher than that of raidz.