Two empty disks, /dev/sdc and /dev/sdd, are to hold a single Btrfs filesystem that keeps a mirrored copy of both data and metadata across the pair, using Btrfs's own multi-device support. Which command creates it?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard medium
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The options
Correct mkfs.btrfs -d raid1 -m raid1 /dev/sdc /dev/sdd
Correct. mkfs.btrfs accepts several devices in one invocation, and -d and -m set the replication profile for data and metadata respectively.
Not correct mkfs.btrfs /dev/sdc; mkfs.btrfs /dev/sdd
Wrong. This makes two separate single-device Btrfs filesystems with no relationship to each other and no mirroring.
Not correct mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdc /dev/sdd && mkfs.btrfs /dev/md0
Wrong for the requirement. It does produce a mirrored result, but the mirroring is done by the md layer beneath a single-device Btrfs, which is not Btrfs's own multi-device support.
Not correct mkfs.ext4 /dev/sdc /dev/sdd
Wrong. mkfs.ext4 formats one device; a second argument is read as the block count, not as another disk, and ext4 has no multi-device mode.
Why
Btrfs spans devices itself rather than sitting on top of md or LVM: mkfs.btrfs takes a list of devices and stripes or mirrors chunks across them according to the profile chosen with -d for data and -m for metadata, with values such as single, dup, raid0, raid1 and raid10. Devices can be added or removed later with `btrfs device add` and `btrfs device delete`, and the whole filesystem is then mounted by naming any one of its members. Compression is a mount option or a per-file property rather than something fixed at mkfs time.
Where this comes from
- Cited
- manual page mkfs.btrfs(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 104 and space the ones you get wrong.
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