ZFS With Gpart partitions

[Jeremy Chadwick]

On Tue, Jan 03, 2012 at 03:38:23PM +0100, Peter Maloney wrote:
> On 01/03/2012 03:34 PM, Peter Maloney wrote:
> > On 01/03/2012 02:01 PM, Dan Carroll wrote:
> >> On 3/01/2012 10:27 PM, krad wrote:
> >>> Just a not you dont appear to be 4k aligned on this drive. As the
> >>> drive capacity is > 1.5 Tb you probably should be. You will also be
> >>> ashift=9 as well. This may or may not be a problem for you. 
> >> That was intentional, as I *thought* these drives were not 4k sector
> >> drives.   I am not sure how I am supposed to tell.   They are WD RE4
> >> drives.
> >> I confess, however to knowing nothing about ashift=9.....   Could you
> >> elaborate?
> > Read this thread:
> >
> > ZFS using 'advanced format drives' with FreeBSD (8.2-RC3)
> > http://forums.freebsd.org/showthread.php?t=21644
> >
> > (and of course don't play around and run the dd command, etc. for disks
> > with valuable data on them)
> >
> And looking at dmesg or /var/log/messages should probably tell you what
> your sector size is.
> 
> eg.
> # dmesg | grep "da2:"
> 
> or
> 
> # grep "da2:" /var/log/messages
> 
> or
> 
> # bunzip2 -c /var/log/messages.1.bz2 | grep "da2:"
> Nov 28 13:59:35 bcnas1 kernel: da2: <ATA ST33000650NS 0002> Fixed Direct
> Access SCSI-6 device
> Nov 28 13:59:35 bcnas1 kernel: da2: 600.000MB/s transfers
> Nov 28 13:59:35 bcnas1 kernel: da2: Command Queueing enabled
> Nov 28 13:59:35 bcnas1 kernel: da2: 2861588MB (5860533168 *512 byte
> sectors*: 255H 63S/T 364801C)

This is incorrect.  Most 4KB sector drives advertise a logical sector
size of 512 (this is to maintain/guarantee full compatibility with older
OSes and existing software), while sometimes advertising a physical
sector size of 4096.  Comparatively, Intel SSDs advertise both a logical
and physical sector size of 512, even though we all know better.

Use either "camcontrol identify" or "camcontrol inquiry" (which command
depends on if you're using SATA-via-CAM or native SCSI) to find out.  If
this doesn't work for you, try using smartmontools (if there's a
difference between logical/physical it will display both, otherwise
it'll say "logical/physical" literally).

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                   Mountain View, CA, US |
| Making life hard for others since 1977.               PGP 4BD6C0CB |