Re: [gentoo-user] [OT] Using an odd number of drives in ZFS RaidZ

[Frank Steinmetzger]

Am Wed, Jun 30, 2021 at 09:45:13PM +0100 schrieb Neil Bothwick:
> On Tue, 29 Jun 2021 15:56:49 +0200, Frank Steinmetzger wrote:
>
> > I reached 80 % usage (which is the recommended maximum for ZFS) and am
> > now evaluating my options for the coming years.
> > 1) Reduce use of space by re-encoding. My payload is mainly movies,
> > among which are 3 TB of DVDs which can be shrunk by at least ⅔ by
> > re-encoding. → this takes time and computing effort, but is a long-term
> > goal anyway. 2) Replace all drives with bigger ones. There are three
> > counter arguments:
> >    • 1000 € for four 10 TB drives (the biggest size available w/o
> > helium)
> >    • they are only available with 7200 rpm (more power, noise and heat)
> >    • I am left with four perfectly fine 6 TB drives
> > 3) Go for 4+2 RaidZ2. This requires a bigger case (with new PSU due to
> >    different form factor) and a SATA expansion card b/c the Mobo only
> > has six connectors (I need at least one more for the system drive),
> > costing 250 € plus drives.
> > 4) Convert to RaidZ1. Gain space of one drive at the cost of
> > resilience. I can live with the latter; the server only runs
> > occasionally and not for very long at a time. *** This option brings me
> > to my question above, because it is easy to achieve and costs no €€€.
>
> 5) (or 3a) Add an eSATA card and expand the RAID with external drives.
>    That way you can stick with 6TB drives.

Antlist made a similar suggestion using external USB, and I gave a more
detailed answer in reply to his mail.

Your proposal, though different regarding filesystem setup, has the same
drawbacks: I am dependent on an external case with its own power supply.
Having everything in one case is very convenient when I want to take the
data on a visit to someone – and it keeps my flat cleaner. :D

I actually looked at external enclosures that I could simply hook up to a
host computer, which then does all the work of speaking to the individual
disks. The problems with that:
- The host needs ECC RAM. NUC-Class devices don’t support that. Even most
  consumer boards don’t (at least officially).
- USB is not suitable for RAID because it lacks protocol features in case of
  errors.
- It’s also a costly endeavour.

I found exactly one case that can hold 6 disks – it cost almost 700 € and
only speaks firewire, which none of my hosts do. My NAS hardware was
actually cheaper than that, including server-grade Mobo, 16 GIG of ECC RAM,
a Gold-rated PSU, and an i3 with custom cooler.

Tata.

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