gvinum raid5 vs. ZFS raidz

Paul Kraus paul at kraus-haus.org
Sat Aug 30 23:07:43 UTC 2014

On Aug 29, 2014, at 21:47, Scott Bennett <bennett at sdf.org> wrote:

> Paul Kraus <paul at kraus-haus.org> wrote:


>> I have been testing with a bunch of 2TB (3 HGST and 1 WD). I have been using ZFS and it has not reported *any* checksum errors.
>     What sort of testing?  Unless the data written with errors are read back,
> how would ZFS know about any checksum errors?  Does ZFS implement write-with-
> verify?  Copying some humongous file and then reading it back for comparison
> (or, with ZFS, just reading them) ought to bring the checksums into play.  Of
> course, a scrub should do that, too.

I typically run a scrub on any new drive after writing a bunch of data to it, specifically to look for infant mortality :-)

>     I have never bought the enterprise-grade drives--though I may begin doing
> so after having read the information you've brought up here--so the difference
> in drive quality at the outset may explain why your results so far have been
> so much better than mine.

Don’t go by what *I* say, go the manufacturer’s web sites and download and read the full specifications on the drives you are looking at. None of the sales sites (Newegg, CDW, etc.) post the full specs, yet they are all (still) available from the Seagate / Western Digital / HGST etc. web sites.

I am just starting to play with a different WD Enterprise series, so far all my testing (and use) has been with the RE series, I just got two 1TB SE series (which are also 5 year warranty and claim to be Enterprise grade, rated for 24x7 operation). I put them into service today and expect to be loading data on them tomorrow or Monday. So now I will have Seagate ES, ES.2, HGST Ultrastar (various P/N), and WD RE, SE drives in use.


>>> If so, try copying a 1.1 TB
>>> file to one of them, and then trying comparing the copy against the original.
>> Hurmmm. I have not worked with individual files that large. What filesystem are you using here? 
>     At the moment, all of my file systems on hard drives are UFS2.

I wonder if it an issue with a single file larger than 1TB … just wondering out loud here.


>     My expectation is that I will end up contacting one or more manufacturers
> to try to replace at least two drives based on whatever ZFS detects, but I
> would be glad to be mistaken about that for now.  If two are that bad, then
> I hope that ZFS can keep things running until the replacements show up here.

I have never had to warranty a drive for uncorrectable errors, they have been a small enough percentage that I did not worry about them, and when the error rate gets big enough other things start going wrong as well. At least that has been my experience.

Paul Kraus
paul at kraus-haus.org

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