Re: [MooseFS-Users] Real experiences from real users

[Gandalf C. <gan...@gm...>]

Il giorno mar 22 mag 2018 alle ore 19:28 Marin Bernard <li...@ol...>
ha scritto:
> So does Proxmox VE.

Not all server are using proxmox.
Proxmox repackage ZFS on every release, because they support it.
If you have to mantain multiple different system, using DKMS is more prone
to error
than without. A small kernel upgrade could break everything.

> That's a myth. ZFS never required ECC RAM, and I run it on boxes with
> as little as 1GB RAM. Every bit of it can be tuned, including the size
> of the ARC.

Is not a myth. Is the truth. ECC RAM is not required to run ZFS, but you
won't be sure
that what are you writing to disks (and checksumming) is exactly the same
you received.

In other words, without ECC RAM you could experience in memory data
corruption and then
you will write corrupted data (with a proper checksum), so that ZFS will
reply with corrupted data.

ECC is not mandatory, but highly suggested.
Without ECC you'll fix the bit-rot, but you are still subject to in-memory
corruption,
so, the original issue (data corruption) is still unfixed and ZFS can't do
nothing if data is
corrupted before ZFS.

> Checksumming and duplication (ditto blocks) of pool metadata are NOT
> provided by the master. This is a much appreciated feature when you
> come from an XFS background where a single urecoverable read can crash
> an entire filesystem. I've been there before; never ever!

At which pool metadata are you referring to ?
Anyway, I hate XFS :-) I had multiple failures......

> MooseFS background verification may take months to check the whole
> dataset

True.

> ZFS does scrub a whole chunkserver within a few hours, with
> adaptive, tunable throughput to minimize the impact on the cluster.

Is not the same.
When ZFS detect a corruption, it does nothing without a RAID. it simply
discard data
during a read. But if you are reading a file, MooseFS will check the
checksum automatically
and does the same.

Anyway, even if you scrub the whole ZFS pool, you won't get any advantage,
ZFS is unable
to recover by itself (without raid) and MooseFS is still unaware of
corruption.

Ok, chunk1 is corrupted, ZFS detected it during a scrub. And now ?
ZFS doesn't have any replica to rebuild from.
MooseFS is unaware of this because their native scrub takes months and
no one is reading that file from a client (forcing the checksum
verification).
So? Which solution do you have ?