On Sun, Mar 2, 2014 at 12:46 AM, Jean-Yves Avenard <jyaven...@gmail.com>wrote:

> On 28 February 2014 20:32, Philip Robar <philip.ro...@gmail.com> wrote:
> cyberjock is the biggest troll ever, not even the people actually
> involved with FreeNAS (iX system) knows what to do with him. He does
> spend an awful amount of time on the freenas forums helping others and
> as such tolerate him on that basis..
> Otherwise, he just someone doing nothing, with a lot of time on his
> hand and spewing the same stuff over and over simply because he has
> heard about it.

Well, that's at odds with his claims of how much time and effort he has put
into learning about ZFS and is basically an ad hominem attack, but since
Daniel Becker has already cast a far amount of doubt on both the scenario
and logic behind cyberdog's EEC vs non-ECC posts and his understanding of
architecture of ZFS I'll move on.

> Back to the ECC topic; one core issue to ZFS is that it will
> specifically write to the pool even when all you are doing is read, in
> an attempt to correct any data found to have incorrect checksum.
> So say you have corrupted memory, you read from the disk, zfs believes
> the data is faulty (after all, the checksum will be incorrect due to
> faulty RAM) and start to rewrite the data. That is one scenario where
> ZFS will corrupt an otherwise healthy pool until its too late and all
> your data is gone.
> As such, ZFS is indeed more sensitive to bad RAM than other filesystem.

So, you're agreeing with cyberdog's conclusion, just not the path he took
to get there.

> Having said that; find me *ONE* official source other than the FreeNAS

forum stating that ECC is a minimal requirements (and no a wiki
> written by cyberjock doesn't count). Solaris never said so, FreeBSD
> didn't either, nor Sun.

So if a problem isn't documented, it's not a problem?

Most Sun/Solaris documentation isn't going to mention the need for ECC
memory because all Sun systems shipped with ECC memory.
FreeBSD/PC-BSD/FreeNAS/NAS4Free/Linux in turn derive from worlds where ECC
memory is effectively nonexistent so their lack of documentation may stem
from a combination of the ZFS folks just assuming that you have it and the
distro people not realizing that you need it. FreeNAS's guide does state
pretty strongly that you should use ECC memory. But if you insist: from
"Oracle Solaris 11.1 Administration: ZFS File Systems", "Consider using ECC
memory to protect against memory corruption. Silent memory corruption can
potentially damage your data." [1]

It seems to me that if using ZFS without ECC memory puts someone's data at
an increased risk over other file system then they ought to be told that so
that they can make an informed decision. Am I really being unreasonable
about this?

> Bad RAM however has nothing to do with the occasional bit flip that
> would be prevented using ECC RAM. The probability of a bit flip is
> low, very low.

You and Jason have both claimed this. This is at odds with papers and
studies I've seen mentioned elsewhere. Here's what a little searching found:

Soft Error: https://en.wikipedia.org/wiki/Soft_error
Which says that there are numerous sources of soft errors in memory and
other circuits other than cosmic rays.

ECC Memory: https://en.wikipedia.org/wiki/ECC_memory
States that design has dealt with the problem of increased circuit density.
It then mentions the research IBM did years ago and Google's 2009 report
which says:

The actual error rate found was several orders of magnitude higher than
previous small-scale or laboratory studies, with 25,000 to 70,000 errors
per billion device hours per mega*bit* (about 2.5-7 × 10-11 error/bit·h)(i.e.
about 5 single bit errors in 8 Gigabytes of RAM per hour using the top-end
error rate), and more than 8% of DIMM memory modules affected by errors per

So, since you've agreed that ZFS is more vulnerable than other file systems
to memory errors, and Google says that these errors are a lot more frequent
than most people think that they are then the question becomes just how
much more vulnerable is ZFS and is the extent of the corruption likely to
be wider or more catastrophic than on other file systems?


[1] Oracle Solaris 11.1 Administration: ZFS File Systems:


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