Re: ZFS performance (was: Re: deduplicating file systems: VDO withDebian?)
On Thu, 2022-11-10 at 23:05 -0500, Michael Stone wrote:
> On Thu, Nov 10, 2022 at 06:55:27PM +0100, hw wrote:
> > On Thu, 2022-11-10 at 11:57 -0500, Michael Stone wrote:
> > > On Thu, Nov 10, 2022 at 05:34:32PM +0100, hw wrote:
> > > > And mind you, SSDs are *designed to fail* the sooner the more data you
> > > > write
> > > > to
> > > > them. They have their uses, maybe even for storage if you're so
> > > > desperate,
> > > > but
> > > > not for backup storage.
> > >
> > > It's unlikely you'll "wear out" your SSDs faster than you wear out your
> > > HDs.
> > >
> >
> > I have already done that.
>
> Then you're either well into "not normal" territory and need to buy an
> SSD with better write longevity (which I seriously doubt for a backup
> drive) or you just got unlucky and got a bad copy (happens with
> anything) or you've misdiagnosed some other issue.
>
Why would anyone use SSDs for backups? They're way too expensive for that.
So far, the failure rate with SSDs has been not any better than the failure rate
of hard disks. Considering that SSDs are supposed to fail less, the experience
with them is pretty bad.
There was no misdiagnosis. Have you ever had a failed SSD? They usually just
disappear. I've had one exception in which the SDD at first only sometimes
disappeared and came back, until it disappeared and didn't come back.
There was no "not normal" territory, either, unless maybe you consider ZFS cache
as "not normal". In that case, I would argue that SSDs are well suited for such
applications because they allow for lots of IOOPs and high data transfer rates,
and a hard disk probably wouldn't have failed in place of the SSD because they
don't wear out so quickly. Since SSDs are so well suited for such purposes,
that can't be "not normal" territory for them. Perhaps they just need to be
more resilient than they are.
You could argue that the SSDs didn't fail because they were worn out but for
other reasons. I'd answer that it's irrelevant for the user why exactly a disk
failed, especially when it just disappears, and that hard disks don't fail
because the storage media wears out like SSDs do but for other reasons.
Perhaps you could buy an SSD that withstands being written to it better. The
question then is if that's economical. It would also be based on the assumption
that SSDs don't so much fail for other reasons than the storage media being worn
out. Since all the failed SSDs have disappeared, I have to assume that they
didn't fail because the storage media was worn out but for other reasons.
Considering that, SSDs generally must be of really bad quality for that to
happen, don't you think?
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