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Re: Btrs vs ext4. Which one is more reliable?




Hello,

On Fri, Jul 28, 2017 at 04:27:32PM +0200, Dan wrote:
> I have a NFS4 server with ext4. I'm moving to Debian Stretch. I wonder if I
> should switch to Btrfs.

I personally wouldn't. I do use btrfs at home and wish I didn't,
will be moving away from it soon.

Take a look at the archives of the linux-btrfs list and note how
many threads there still are involving phantom -ENOSPC issues,
problems where filesystems cannot be mounted unless kernel and
tools are updated to bleeding edge versions, and occasionally
outright data loss.

I haven't had data loss but I've had the -ENOSPC problems and also
situations where a dead device can't be removed and a replacement
added without rebooting and upgrading kernel. These are not things I
expect from a redundant filesystem and so for me it's not ready yet.

    https://www.mail-archive.com/linux-btrfs@xxxxxxxxxxxxxxx/

> I like the checksum feature to prevent silent corruption.

You could consider ZFS on Linux.

    http://zfsonlinux.org/

> My understanding is that the only thing that prevents silent corruption in
> ext4 is the hard drive CRC (Cyclic Redundancy Check Error). Is that enough
> for a server?

No, not with multi-terabyte devices. CRC doesn't detect well enough,
also errors can happen at different places that CRC can't always
detect.

> I do backups very often, I don't mind if the hard drive dies,
> but I don't want silent corruption.

Error-checking filesystem isn't a substitute for backups so you'll
always need those. Make sure you have historical versions so you can
check for silent corruption.

Having RAID and scrubbing it regularly helps. It will at least spot
mismatches. The mdadm package on Debian does that by default once
per month and I could recommend making that more often if it doesn't
cause you performance issues. Also note that if you only have a two
way mirror and you find out there are mismatches, you may not be
able to tell which mirror has the correct data. Forcing md to fix it
will cause it to pick one side at random.

I'm sure there will be plenty of people who have used btrfs for
years and had no issue. But I didn't do anything wrong with it, did
have issues, and so do a lot of other posters to linux-btrfs.
Nothing is perfect but the amount of problems I still see there is
enough cause for concern to me.

The worst I've seen on the zfsonlinux list in the last couple of
years is people reporting abnormally low performance in their
configuration.

Cheers,
Andy

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