gvinum raid5 vs. ZFS raidz

Scott Bennett bennett at sdf.org
Tue Aug 26 06:42:38 UTC 2014

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
> > 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.
> >     While I was out of town, I came across a trade magazine article that
> > said that as the areal density of bits approaches the theoretical limit for
> > the recording technology currently in production, the error rate climbs ever
> > more steeply, and that the drives larger than 1 TB are now making that effect
> > easily demonstrable. :-(
> It took perpendicular recording to make >1TB drives possible at all. 
> >  The article went on to describe superficially a new
> > recording technology due to appear on the mass market in 2015 that will allow
> > much higher bit densities, while drastically improving the error rate (at
> > least until densities eventually close in on that technology's limit).  So
> > it may turn out that next year consumers will begin to move past the hump in
> > error rates and will find that hardware RAID will have become acceptably safe
> > once again.  The description of the new recording technology looked like a
> > really spiffed up version of the magneto-optical disks of the 1990s.  In the
> > meantime, though, the current crops of large-capacity disks apparently
> > require software solutions like ZFS to preserve data integrity.
> I do not know the root cause of the uncorrectable errors, but they seem to vary with product line and not capacity. Whether that means the Enterprise drives with the order of magnitude better uncorrectable error rate has better coatings on the platters or better heads or better electronics or better QC I do not know. So I don?t know how mud this new technology will effect those errors.

     I guess we'll have to see what people report after the new technology
appears on the market next year.

                                  Scott Bennett, Comm. ASMELG, CFIAG
* Internet:   bennett at sdf.org   *xor*   bennett at freeshell.org  *
* "A well regulated and disciplined militia, is at all times a good  *
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