[OpenIndiana-discuss] ECC question

[taemun]

ECC RAM provides a mechanism by which the data stored can be checked, and
given a small enough error, repaired. Standard RAM doesn't provide this.

Buffering is done at the hardware level to increase throughput (gigabytes
per second) at the expense of latency (nano seconds per operation). Your
choice of motherboard/chipset/cpu will generally dictate if you want ECC
FBDIMM's or just ECC DDR3.

In the context of ZFS, ECC is a good thing because a bit error in RAM could
potentially break a pool - if it occurred just before an important block was
written out. Far more likely, is that it could cause a checksum to be
computed incorrectly before being written out, which would have the effect
of making an unfixable block in the pool. This doesn't really matter, unless
you hold every bit to be sacred (which may be true, in some business
environments.

Note that ZFS isn't intrinsically any more likely to die from a bad bit in
RAM than any given file system, but it is going to be able to *tell you when
it occurs*.

I'd note that AMD's cheap CPUs support ECC, whilst in the Intel camp you
need to get something with Xeon written on it as a starting point. Their
websites can provide information on which units do and don't, and what type
of RAM is appropriate for each CPU.

Cheers,

On 21 February 2011 01:31, Harry Putnam <reader at newsguy.com> wrote:

> ECC memory or not, buffered or not.  What does it do/mean
>
> At risk of being stoned for bringing this up again, I am not finding
> threads from the past that provide (to me) a basic idea of what the
> terms means and what the concepts do.
>
> I'm sure this will sound horribly illiterate in computer tech, but
> that is the state of things so here it is:
>
> First, how does ECC and buffered terms fit together?
>
> What is the advantage/disadvantage in practical terms
>
> What does an ignorant end user need to now about this to make sure of
> getting the best hardware when building a system dedicated to zfs
> server?
>
>
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