ECC support

[alex.burlyga.ietf alex.burlyga.ietf]

On Tue, Sep 15, 2015 at 3:52 PM, Igor Mozolevsky <igor at hybrid-lab.co.uk> wrote:
> On 15 September 2015 at 23:34, Jim Thompson <jim at netgate.com> wrote:
>
> <snip>
>
>
>> I think you’ll find that the default for ‘scrub’ is off on most (perhaps
>> all) boards.  There are reasons, and these relate directly to
>> “significantly diminish system performance”, (above), as well as the
>> greatly increased RAM sizes in use today.
>>
>
> Perhaps I missed something- what point is it that you're trying to make? I
> was saying that scrubbing aims to remove errors at the source (cf. "on
> demand") and prevent multi-bit errors that become detectable but
> irrecoverable, or worse, undetectable. Get hit by a few of the latter two
> at "interesting" points and you'd wish that scrubbing were on!
>
> And seriously, ECC scrubbing is slow but ZFS (or even hardware RAID)
> scrubbing is lightning fast??! C'mon are we going for data integrity or
> speed here?!

If I remember correctly enabling Patrol Scrub guaranties that each
address gets hit once per 24 hours. So on 128GB system you are
generating maybe 1-2MiB/s of reads. I'd say it's a good trade-off if
you bothered to put ECC memory in.

>
> ’Scrub' was popular about a decade ago, when DDR2 RAM was around $100/GB.
>> DDR3-1600 is about $6/GB today.
>>
>
> Yup- with a much higher density of smaller memory bits! ;-)
>
> --
> Igor M.
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