RAID1C34 new for BTRFS
https://btrfs.wiki.kernel.org/index.php/Main_Page
https://btrfs.wiki.kernel.org/index....age/mkfs.btrfs
PROFILES
There are the following block group types available:
<tbody> </tbody>
Note 2: It’s not recommended to use 2 devices with RAID5. In that case, parity stripe will contain the same data as the data stripe, making RAID5 degraded to RAID1 with more overhead.
Note 3: It’s also not recommended to use 3 devices with RAID6, unless you want to get effectively 3 copies in a RAID1-like manner (but not exactly that).
Note 4: Since kernel 5.5 it’s possible to use RAID1C3 as replacement for RAID6, higher space cost but reliable.
linux v5.5 (Jan 2020)
- new block group profiles: RAID1 with 3- and 4- copies
- RAID1 in btrfs has always 2 copies, now add support for 3 and 4
- this is an incompat feature (named RAID1C34)
- recommended use of RAID1C3 is replacement of RAID6 profile on metadata, this brings a more reliable resiliency against 2 device loss/damage
PROFILES
There are the following block group types available:
<tbody> </tbody>
| Profile | Redundancy | Space utilization | Min/max devices | ||
| Copies | Parity | Striping | |||
| single | 1 | 100% | 1/any | ||
| DUP | 2 / 1 device | 50% | 1/any (see note 1) | ||
| RAID0 | 1 to N | 100% | 2/any | ||
| RAID1 | 2 | 50% | 2/any | ||
| RAID1C3 | 3 | 33% | 3/any | ||
| RAID1C4 | 4 | 25% | 4/any | ||
| RAID10 | 2 | 1 to N | 50% | 4/any | |
| RAID5 | 1 | 1 | 2 to N-1 | (N-1)/N | 2/any (see note 2) |
| RAID6 | 1 | 2 | 3 to N-2 | (N-2)/N | 3/any (see note 3) |
Warning: It’s not recommended to create filesystems with RAID0/1/10/5/6 profiles on partitions from the same device. Neither redundancy nor performance will be improved.
Note 1: DUP may exist on more than 1 device if it starts on a single device and another one is added. Since version 4.5.1, mkfs.btrfs will let you create DUP on multiple devices without restrictions.Note 2: It’s not recommended to use 2 devices with RAID5. In that case, parity stripe will contain the same data as the data stripe, making RAID5 degraded to RAID1 with more overhead.
Note 3: It’s also not recommended to use 3 devices with RAID6, unless you want to get effectively 3 copies in a RAID1-like manner (but not exactly that).
Note 4: Since kernel 5.5 it’s possible to use RAID1C3 as replacement for RAID6, higher space cost but reliable.