[Info-vax] VMS - The new file system. What do we know about it?...

[johnwallace4 at yahoo.co.uk]

On Tuesday, 15 November 2016 12:26:04 UTC, Paul Sture  wrote:
> On 2016-11-15, Dirk Munk <munk at home.nl> wrote:
> > Paul Sture wrote:
> >> On 2016-11-14, Michael Moroney <moroney at world.std.spaamtrap.com> wrote:
> >>> Dirk Munk <munk at home.nl> writes:
> >>>
> >>>> Modern disks of course use the Advanced Format structure, with 4kB
> >>>> blocks/sectors. Using arbitrary 512 byte blocks is possible, but not
> >>>> very good for performance. Is that taken into consideration?
> >>>
> >>> That will have to be a separate project.  From what someone here told me
> >>> other OS's (Linux, Windoze) still use 4K block drives in 512 byte block
> >>> emulation mode.  Can anyone verify/refute this?
> >>
> >> If you look at the WD Red series of disks you will find that the 1TB,
> >> 2TB and 3TB models are 4K block capable but lie to the OS when asked
> >> if they support that.  Reading between the lines, this was to support
> >> the large numbers of Windows Server 2003 & XP systems still in use
> >> when this series of disks was released.
> >>
> >> There are O/S specific ways of overriding this, and with an OS which
> >> supports 4K disks, the main hurdle can be getting the disk formatted
> >> with 4K blocks.  Once formatted correctly, 4K will be used.
> >
> > I'm not quite sure what you mean. An OS always uses logical blocks when 
> > formatting a disk, so does VMS. If you're using disk with 4kB sectors, 
> > you have to make sure your logical blocks are a multiple of 4kB, and the 
> > partitions always start at a sector boundary.
> 
> Please see
> 
> <http://wiki.illumos.org/display/illumos/ZFS+and+Advanced+Format+disks>
> 
> In Paragraph 2: 
> 
>     If the disk reports that the physical sector size is 512 bytes, then
>     ZFS will use an internal sector size of 512 bytes. The problem is
>     that some HDDs misrepresent 4KB sector disks as having a physical
>     sector size of 512 bytes. The proper response should be that the
>     logical sector size is 512 bytes and the physical sector size is
>     4KB.  ...  In some cases, the HDD vendors advertise the disks as
>     "emulating 512 byte sectors" or "512e", ...
> 
> Also see the summary in para 5.
> 
> And using the command at the bottom of the page on my system, I get
> this>
> 
>     zdb | egrep 'ashift| name'
>     name: 'backup'
>             ashift: 9
>     name: 'zones'
>             ashift: 12
> 
> Where 'zones' is a mirrored pair of WD Red 3TB disks, and 'backup'
> is a mirrored pair of 1TB external USB disks bought in 2010.
> 
> > Modern disk partitioning tools will always make sure partitions start at 
> > a multiple of 1MB, which of course is also a multiple of 4kB.
> 
> Can you give some examples of 'Modern disk partitioning tools'?
> 
> One thing I noticed when XP was still around was that the Linux
> partitioning tools didn't set up disks entirely correctly for Windows. 
> One clue may be the comment about the "XP Jumper" to offset LBA
> addresses by 1" mentioned in the above article.  Dunno, but there are
> still a lot of the smaller capacity disks out there whose design dates
> back to 2010 or before, particularly at the consumer level.
> 
> 
> -- 
> The optimist believes we're living in the best of all possible worlds
> and the pessimist is afraid that's true.

Ah, someone who's been around and got out a bit, excellent.

Doesn't this whole "how big is a block" business sound remarkably
familiar?

Like when flash disk first started being a thing, for example?

Just askin'.