gvinum raid5 vs. ZFS raidz

Paul Kraus paul at kraus-haus.org
Thu Aug 28 14:28:08 UTC 2014

On Aug 28, 2014, at 2:36, Scott Bennett <bennett at sdf.org> wrote:

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

>> 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?

I suppose my point was that an operation that is NOT flagged by the drive as failing and DOES return faulty data is, by definition, an uncorrectable error (as far as the drive is concerned). The point is that an uncorrectable error (from the drive standpoint) is just that, an error that the drive CANNOT detect.

>     Are you using any drives larger than 1 TB?

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.

I have put one of the 4 into production service (I needed a replacement for a failed 1TB and did not have any more 1TB in stock). It has been running for a couple weeks now with no checksum errors reported. My zpool is 5 x 1TB RAIDz2 and it has about 2TB of data on it right now.

>  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? 

> 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.

If you use ZFS on these drives and copy the same file do you get any checksum errors?

Paul Kraus
paul at kraus-haus.org

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