[Nottingham] Growing a RAID 1

[Andy Smith]

Hello,

On Thu, Jan 26, 2023 at 09:31:29AM +0000, Michael Simms via Nottingham wrote:
> Be really careful on BTRFS raid. Last I checked it was still "unfit for
> purpose" and the place I worked lost a lot of data due to raid 5 failures.

I've also used btrfs quite a bit. I'm not entirely happy with it,
but mostly from an availability point of view rather than
reliability.

The warning / bad reputation with btrfs's RAID profiles are for
parity profiles like RAID-5 and RAID-6; the mirro and stripe
profiles (0,1,10) are considered safe.

I haven't ever lost any data due to btrfs bugs or deficiencies, but
I did encounter some situations that required a reboot to sort out a
failed drive when I think that should not have been the case.

One particular gotcha with btrfs is that unlike MD RAID, if it's
degraded it won't mount the filesystem after a reboot! You have to
force it to with a mount option, and then some of the new data that
is written will not be redundant.

With MD RAID, an array remains fully operational while degraded,
then you replace the failed drive and the array resyncs so there's
redundancy again. With btrfs a degraded filesystem won't mount; you
have to force it to, and then after you've added back enough drives
for redundancy you have to run a "balance" over it to make redundant
copies of any data that was written while it was degraded.

> On 26/01/2023 09:18, J I via Nottingham wrote:
> > I actually made the leap to BTRFS for the RAID, a couple of subvolumes
> > and it all went very smoothly.

I take it that with just the two drives you went for RAID-1 profile?

Compression is also a good feature of btrfs. Although if you have
plenty of space for your anticipated needs then there is little
point.

> > Old (11.5 year old!) drives are out and I am now seriously considering
> > flipping the other server.

Join the block device leader board:

https://gist.github.com/grifferz/64808f61079fe610c6f21f03ac7fd1aa

$ ~/src/blkleaderboard/blkleaderboard.sh
     sdd 114600 hours (13.07 years) 0.29TiB ST3320620ASg
     sdb 109964 hours (12.54 years) 0.29TiB ST3320620ASg
     sda 108433 hours (12.36 years) 0.29TiB ST3320620ASg
     sdk  71645 hours ( 8.17 years) 2.73TiB WDC WD30EZRX-00Dg
     sdh  60754 hours ( 6.93 years) 0.91TiB Hitachi HUA72201g
     sde  40482 hours ( 4.61 years) 0.91TiB SanDisk SDSSDH31g
     sdc  33915 hours ( 3.86 years) 0.29TiB ST3320418ASg
     sdf  23494 hours ( 2.68 years) 1.82TiB Samsung SSD 860g
     sdj  23373 hours ( 2.66 years) 1.75TiB KINGSTON SUV5001g
     sdg  17803 hours ( 2.03 years) 1.75TiB KINGSTON SUV5001g
     sdi   4332 hours ( 0.49 years) 0.45TiB ST500DM002-1BD14g

(That's power on time, not just age!)

Just a fileserver at home of course. Would not want to be using 15+
year old drives in anything important. 😀

Cheers,
Andy

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