Re: PostgreSQL advocacy

Jernigan, Kevin wrote:
>On 3/24/16, 3:09 PM, "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at> wrote:
>>> Disk is only a single point of failure in RAC if you configure non-redundant storage.
>>> In general, Oracle recommends triple mirroring to protect against disk failures,
>>> as they have had many experiences over the years where customers with mirrored disks
>>> would see consecutive disk failures within short periods of time.
>>
>>The single point of failure in Oracle RAC is the ASM file system.
>
> Only if you misconfigure ASM for RAC: with RAC, an ASM instance will run on every RAC node,
> and if the ASM instance fails on any one node, the RAC instance on that node will go down,
> but the RAC instances on the other nodes will continue to run - so the database will remain
> accessible, though with fewer processors available.
>
> If you configure ASM to implement at least dual mirroring for storage - and I’m pretty sure
> Oracle intentionally makes it hard to configure ASM without mirroring - then ASM will continue
> run through any single disk failure.

I think you missed my point.

I am not talking about disk failure, but about some failure (possibly a software bug or
a combination of hardware problem and software weakness) that causes the on-disk
data to be corrupted. File system corruption.

Mirroring will only mirror such a corruption, and multiple ASM instances that all access
the same corrupted data won't help either.

Of course Oracle says that ASM is so simple and bullet-proof that this cannot happen,
but claiming that something cannot fail is not good enough.
RAC is a shared storage system, and that shared storage is a single point of failure.

Yours,
Laurenz Albe