diff options
| -rw-r--r-- | Documentation/mkfs.btrfs.asciidoc | 16 | ||||
| -rw-r--r-- | utils.c | 10 |
2 files changed, 20 insertions, 6 deletions
diff --git a/Documentation/mkfs.btrfs.asciidoc b/Documentation/mkfs.btrfs.asciidoc index 98fe694b..7d19a146 100644 --- a/Documentation/mkfs.btrfs.asciidoc +++ b/Documentation/mkfs.btrfs.asciidoc @@ -263,18 +263,26 @@ There are the following block group types available: .2+^.<h| Profile 3+^.^h| Redundancy .2+^.<h| Min/max devices ^.^h| Copies ^.^h| Parity ^.<h| Striping | single | 1 | | | 1/any -| DUP | 2 / 1 device | | | 1/any ^(see note)^ +| DUP | 2 / 1 device | | | 1/any ^(see note 1)^ | RAID0 | | | 1 to N | 2/any | RAID1 | 2 | | | 2/any | RAID10 | 2 | | 1 to N | 4/any -| RAID5 | 1 | 1 | 2 to N - 1 | 2/any -| RAID6 | 1 | 2 | 3 to N - 2 | 3/any +| RAID5 | 1 | 1 | 2 to N - 1 | 2/any ^(see note 2)^ +| RAID6 | 1 | 2 | 3 to N - 2 | 3/any ^(see note 3)^ |============================================================= -'Note:' DUP may exist on more than 1 device if it starts on a single device and +'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. +'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). +N-copies RAID1 is not implemented. + DUP PROFILES ON A SINGLE DEVICE ------------------------------- @@ -3280,6 +3280,7 @@ int test_num_disk_vs_raid(u64 metadata_profile, u64 data_profile, u64 dev_cnt, int mixed, int ssd) { u64 allowed = 0; + u64 profile = metadata_profile | data_profile; switch (dev_cnt) { default: @@ -3294,8 +3295,7 @@ int test_num_disk_vs_raid(u64 metadata_profile, u64 data_profile, allowed |= BTRFS_BLOCK_GROUP_DUP; } - if (dev_cnt > 1 && - ((metadata_profile | data_profile) & BTRFS_BLOCK_GROUP_DUP)) { + if (dev_cnt > 1 && profile & BTRFS_BLOCK_GROUP_DUP) { warning("DUP is not recommended on filesystem with multiple devices"); } if (metadata_profile & ~allowed) { @@ -3315,6 +3315,12 @@ int test_num_disk_vs_raid(u64 metadata_profile, u64 data_profile, return 1; } + if (dev_cnt == 3 && profile & BTRFS_BLOCK_GROUP_RAID6) { + warning("RAID6 is not recommended on filesystem with 3 devices only"); + } + if (dev_cnt == 2 && profile & BTRFS_BLOCK_GROUP_RAID5) { + warning("RAID5 is not recommended on filesystem with 2 devices only"); + } warning_on(!mixed && (data_profile & BTRFS_BLOCK_GROUP_DUP) && ssd, "DUP may not actually lead to 2 copies on the device, see manual page"); |