Re: Btrfs and integration with GNU ++

[Eric Sandeen <sandeen@redhat.com>]

On 5/17/15 2:33 PM, Roy Sigurd Karlsbakk wrote:
> Hi all

> Lastly - I just did a small test on a 6 drive RAID-6, turned on
> compression and started cat /proc/zero > testfile - let this run
> until the filesize was 500GB and stopped it. Made some other test
> files and a copy of these with --reflink=auto just for kicks. rm
> test* and waited. While waiting, did a 'echo b > /proc/sysrq-trigger'
> and fsck started on bootup and took a minute or so to complete. Since
> the filesystem is rather small (6x8GB VDEVs on top of ZFS with SSD
> caching, kvm as hypervisor), I wonder how long this fsck job would
> take if it were on a system with, say, 6 4TB drives. RHEL/CentOS7
> just moved to XFS to allow for system crashes without this hour-long
> fsck job, and I somewhat doubt that btrfs will be the chosen one if
> it requires the same amount of time as of ext4.

Others have mentioned this as well, but I'll say it more broadly:

echo b > /proc/sysrq-trigger should not require a fsck on any journaling
filesystem - xfs, ext3, ext4, or btrfs - that's the whole reason you pay
the slight overhead for metadata journaling at runtime, right?

Was it really running a fsck?

-Eric