gvinum raid5 vs. ZFS raidz

Scott Bennett bennett at sdf.org
Thu Aug 28 06:37:08 UTC 2014

Paul Kraus <paul at kraus-haus.org> wrote:
> On Aug 26, 2014, at 2:41, Scott Bennett <bennett at sdf.org> wrote:
> > Paul Kraus <paul at kraus-haus.org> wrote:
> >> On Aug 22, 2014, at 5:40, Scott Bennett <bennett at sdf.org> wrote:
> >>> What I'm seeing here is ~2 KB of errors out
> >>> of ~1.1TB, which is an error rate (in bytes, not bits) of ~1.82e+09, and the
     As I caught and corrected before, the above should have said, "~1.82e-09".

> >>> majority of the erroneous bytes I looked at had multibit errors.  I consider
> >>> that to be a huge change in the actual device error rates, specs be damned.
> >> 
> >> That seems like a very high error rate. Is the drive reporting those errors or are they getting past the drive?s error correction and showing up as checksum errors in ZFS ? A drive that is throwing that many errors is clearly defective or dying.
> > 
> >     I'm not using ZFS yet.  Once I get a couple more 2 TB drives, I'll give
> > it a shot.
> >     The numbers are from running direct comparisons between the source file
> > and the copy of it using cmp(1).  In one case, I ran the cmp twice and got
> > identical results, which I interpret as an indication that the errors are
> > occurring during the writes to the target disk during the copying.
> Wow. That implies you are hitting a drive with a very high uncorrectable error rate since the drive did not report any errors and the data is corrupt. I have yet to run into one of those.

     How would an uncorrectable error be detected by the drive without any
parity checking or hardware-implemented write-with-verify?
     Are you using any drives larger than 1 TB?  If so, try copying a 1.1 TB
file to one of them, and then trying comparing the copy against the original.
Out of the three drives I could test that way, I got that kind of result on
two every time I tried it.  One of the two was a new Samsung (i.e., a
Seagate), and the other was a refurbished Seagate supplied as a replacement
under warranty.  The third got a clean copy the first time and two bytes with
single-bit errors on the second try.  That one was also a refurbished Seagate
provided under warranty.

                                  Scott Bennett, Comm. ASMELG, CFIAG
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