Re: [gentoo-user] OT: btrfs raid 5/6

[Frank Steinmetzger]

On Thu, Dec 07, 2017 at 09:49:29PM +0000, Wols Lists wrote:
> On 07/12/17 21:37, Frank Steinmetzger wrote:
> > Ooooh, I just came up with another good reason for raidz over mirror:
> > I don't encrypt my drives because it doesn't hold sensitive stuff. (AFAIK
> > native ZFS encryption is available in Oracle ZFS, so it might eventually
> > come to the Linux world).
> >
> > So in case I ever need to send in a drive for repair/replacement, noone can
> > read from it (or only in tiny bits'n'pieces from a hexdump), because each
> > disk contains a mix of data and parity blocks.
> >
> > I think I'm finally sold. :)
> > And with that, good night.
>
> So you've never heard of LUKS?
>
> GPT
> LUKS
> MD-RAID
> Filesystem

My new drives are finally here. One of them turned out to be an OEM. -_-
The shop says it will cover any warranty claims and it’s not a backyard
seller either, so methinks I’ll keep it.

To evaluate LUKS, I created the following setup (I just love ASCII-painting
in vim ^^):

┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ tmpfs                                                           ┃
┃ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┃
┃ │  1 GB file  │ │  1 GB file  │ │  1 GB file  │ │  1 GB file  │ ┃
┃ └──────┬──────┘ └──────┬──────┘ └──────┬──────┘ └──────┬──────┘ ┃
┃        V               V               V               V        ┃
┃ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┃
┃ │ LUKS device │ │ LUKS device │ │ LUKS device │ │ LUKS device │ ┃
┃ └──────┬──────┘ └──────┬──────┘ └──────┬──────┘ └──────┬──────┘ ┃
┃        V               V               V               V        ┃
┃ ┌─────────────────────────────────────────────────────────────┐ ┃
┃ │                          RaidZ2                             │ ┃
┃ └─────────────────────────────────────────────────────────────┘ ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛

While dd'ing a 1500 MB file from and to the pool, my NAS Celeron achieved
(with the given number of vdevs out of all 4 being encrypted):

          non-encrypted    2 encrypted   4 encrypted
────────────────────────────────────────────────────
read          1600 MB/s       465 MB/s      290 MB/s
write         ~600 MB/s      ~200 MB/s     ~135 MB/s
scrub time                                   10 s (~ 100 MB/s)

So performance would be juuuust enough to satisfy GBE. I wonder though how
long a real scrub/resilver would take. The last scrub of my mirror, which
has 3.8 TB allocated, took 9¼ hours. Once the z2 pool is created and the
data migrated, I *will* have to do a resilver in any case, because I only
have four drives and they will all go into the pool, but two of which
currently make up the mirror.


I see myself bying an i3 before too long. Talk about first-world problems.
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