GELI reliability

[Modulok]

>> I've used ZFS over GELI in the past, but never had any hardware issues to see how it plays out.

I have no idea on that kind of a setup. If I were you I'd make a test
system, start an scp command to copy some file from another machine,
then start unplugging hard drives. When done, run a diff on the copied
file and the original (or at least a checksum) to see if it worked
out. I'd do it for you and report back, but at the moment I don't have
the hardware to spare.

Let us know how it goes ;-)
-Modulok-

On 2/25/11, Terje Elde <terje at elde.net> wrote:
> Hi,
>
> I'm curious about GELIs theoretical behavior when faced with errors, and
> also any experience anyone might have.
>
> As an example, if I run ZFS with raidz over X drives, then the zpool should
> have no issue surviving the complete loss of a full disk.  Also, the
> familiar "FAILURE - READ_DMA" or READ_DMA48 errors from a disk having a bad
> day should also be no issue, certainly not an issue that would result in
> crash, or worse still, loss of data.
>
> What I'm wondering is how much worse off the data would be if I were to
> slide inn a GELI layer between the physical drives, and the zpool.
>
> That is, if I use GELI directly on the individual drives ( /dev/ada0,
> /dev/ada1 etc), then make a raidz pool on top of the .eli devices (
> /dev/ada0.eli, /dev/ada1.eli etc).
>
> For READ_DMA type errors, I suppose GELI could just forward the same errors
> up the stack, and that'd be that, the errors wouldn't be any more severe
> than what I'd have anyway?
>
> One exception could be if GELI sector size is larger than disk sector size.
> Not being too familiar with GELIs internal workings, I'm not sure that has
> to be the case though.  GELI sectors have a new IV pr. sector, but the
> crypto itself is still done in 128 or 256 bit blocks, so given a single
> faulty disk sector, the rest of the GELI sector could still be read and
> decrypted?  Or are entire GELI sectors faulted if a (smaller) underlaying
> sector is unreadable?
>
> And finally, what if an entire drive dies a cruel and horribly death, all of
> it's data returning to the large bit bucket in the sky?  Would GELI simply
> relay the same errors upstack to ZFS, so ZFS would be able to handle it as
> well as it would have without GELI?
>
>
> I've used ZFS over GELI in the past, but never had any hardware issues to
> see how it plays out.
>
> I'm considering deploying it for more stuff now, and reliability wise, from
> what I know, I could loose very little by using GELI, or it could be time to
> buy napkins, because the risk of a grown man crying while trying to mop up
> spilled bits from the floor is increased significantly.
>
> (backups should avoid the need for tears though, besides, I don't have a
> mop)
>
> Terje
>
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