From b2f78e88052bc0bee56bbf646d245fcfb431a873 Mon Sep 17 00:00:00 2001 From: David Sterba Date: Thu, 22 Jul 2021 20:54:37 +0200 Subject: [PATCH] btrfs: allow degenerate raid0/raid10 The data on raid0 and raid10 are supposed to be spread over multiple devices, so the minimum constraints are set to 2 and 4 respectively. This is an artificial limit and there's some interest to remove it. Change this to allow raid0 on one device and raid10 on two devices. This works as expected eg. when converting or removing devices. The only difference is when raid0 on two devices gets one device removed. Unpatched would silently create a single profile, while newly it would be raid0. The motivation is to allow to preserve the profile type as long as it possible for some intermediate state (device removal, conversion), or when there are disks of different size, with raid0 the otherwise unusable space of the last device will be used too. Similarly for raid10, though the two largest devices would need to be the same. Unpatched kernel will mount and use the degenerate profiles just fine but won't allow any operation that would not satisfy the stricter device number constraints, eg. not allowing to go from 3 to 2 devices for raid10 or various profile conversions. Example output: # btrfs fi us -T . Overall: Device size: 10.00GiB Device allocated: 1.01GiB Device unallocated: 8.99GiB Device missing: 0.00B Used: 200.61MiB Free (estimated): 9.79GiB (min: 9.79GiB) Free (statfs, df): 9.79GiB Data ratio: 1.00 Metadata ratio: 1.00 Global reserve: 3.25MiB (used: 0.00B) Multiple profiles: no Data Metadata System Id Path RAID0 single single Unallocated -- ---------- --------- --------- -------- ----------- 1 /dev/sda10 1.00GiB 8.00MiB 1.00MiB 8.99GiB -- ---------- --------- --------- -------- ----------- Total 1.00GiB 8.00MiB 1.00MiB 8.99GiB Used 200.25MiB 352.00KiB 16.00KiB # btrfs dev us . /dev/sda10, ID: 1 Device size: 10.00GiB Device slack: 0.00B Data,RAID0/1: 1.00GiB Metadata,single: 8.00MiB System,single: 1.00MiB Unallocated: 8.99GiB Note "Data,RAID0/1", with btrfs-progs 5.13+ the number of devices per profile is printed. Reviewed-by: Qu Wenruo Signed-off-by: David Sterba --- fs/btrfs/volumes.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 8e61307..8526cc3 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -38,7 +38,7 @@ const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = { .sub_stripes = 2, .dev_stripes = 1, .devs_max = 0, /* 0 == as many as possible */ - .devs_min = 4, + .devs_min = 2, .tolerated_failures = 1, .devs_increment = 2, .ncopies = 2, @@ -103,7 +103,7 @@ const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = { .sub_stripes = 1, .dev_stripes = 1, .devs_max = 0, - .devs_min = 2, + .devs_min = 1, .tolerated_failures = 0, .devs_increment = 1, .ncopies = 1, -- 2.7.4