gvinum raid5 vs. ZFS raidz

Paul Kraus paul at kraus-haus.org
Sun Aug 31 17:12:40 UTC 2014

On Aug 31, 2014, at 3:49, Scott Bennett <bennett at sdf.org> wrote:

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

>> I typically run a scrub on any new drive after writing a bunch of data to it, specifically to look for infant mortality :-)
>     Looks like a good idea.  Whenever I get the raidz2 set up and some
> sizable amount of data loaded into it, I intend to do the same.  However,
> because the capacity of the 6-drive raidz2 will be about four times the
> original UFS2 capacity, I suppose I'll need to find a way to expand the
> dump file in other ways, so as to cover the misbehaving tracks on the
> individual drives.

I’m not sure I would worry about exercising the entire range of tracks on the platters, if a platter has a problem (heads or coating) it will likely show up all over the platter. If the problem is specific to a region, I would expect the drive to be able to remap the bad sectors (as we previously discussed).

>> 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.
>     Yes, I understood that from what you had already written.  What I meant
> was that I hadn't been aware that the manufacturers were selling the drives
> divided into two differing grades of reliability.  From now on, the issue
> will be a matter of my budget vs. the price differences.

Sorry If I was being overly descriptive, I am more of a math and science guy than an english guy, so my writing is often not the most clear. When I started buying Enterprise instead of Desktop drives the price difference was under $20 for a $100 drive. The biggest reason I started buying the Enterprise drives is that they are RATED for 24x7 operation, while Desktop are typically designed for 8x5 (but rarely do they say :-) While I do have my desktop and laptop systems setup to spin down the drives when not in use (and I leave some of them booted 24x7), my server(s) run 24x7 and THAT is where I pay for the Enterprise drives. I treat the drives in the laptop / desktop systems as disposable and do NOT keep any important data only on them (I rsync my laptop to the server a couple times per week and use TimeMachine when at the office).


>     Okay.  Thanks again for the info.  Just out of curiosity, where do you
> usually find those Hitachi drives?

Newegg … Once they lean red how to ship drives without destroying them I started buying drives from them :-)


>> I wonder if it an issue with a single file larger than 1TB ? just wondering out loud here.
>     Well, all I can say is that it is not supposed to be.  After all, file
> systems that were very large were the reason for going from UFS1 to UFS2.

I realized that I proposed something ludicrous (the problem with thinking “aloud”), if the FS did not support -files- larger than 1TB, then the write operation would have failed when you got to that point. Yes, I remember FSes that could not handle a -file- larger than 2GB!

Note that there is a difference between the size of a filesystem and the size of the largest -file- that filesystem may contain.


>> 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.
>     I would count yourself very lucky if I were you, although my previous
> remark regarding the difference in reliability grades still holds.

I have not tried to use Desktop drives in a Servers (either my own or a client’s) for well over a decade. I do not remember much about drive failures before that. Back then my need for capacity was growing faster than drives were failing, so I was upgrading before the drives failed. I still have a pile of 9GB SCSI drives (and some 18GB and 36GB) kicking around from those days. Not to mention the drawer full of 500MB (yes, 0.5GB) drives I harvested from an old Sun SS1000 before I sold it … I should have left the drives in it.

Paul Kraus
paul at kraus-haus.org

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