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

[Paul Sture]

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.