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

[Dirk Munk]

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.

Modern disk partitioning tools will always make sure partitions start at 
a multiple of 1MB, which of course is also a multiple of 4kB.

>
> When I did this with SmartOS a year ago for disks destined to hold the
> ZFS filesystem, one technique suggested was to boot from an O/S (e.g.
> FreeBSD) that could do this, another technique on a virgin system was to
> feed the boot command line with "ASHIFT=12". IIRC I got there using
> OmniOS.
>
> The 4TB and above WD Red models correctly report themselves as 4K
> capable.
>
> Do a search for ASHIFT=9 versus ASHIFT=12.  If you think these numbers
> are weird choices, think of powers of 2 :-)
>
>> Also, most VMS IO on itanics is through SAN storage servers, and they
>> are the ones that have to directly deal with 4K blocks.  I don't know
>> if storage servers themselves present themselves as using 4K blocks.
>>
>> Of course there are directly attached SCSI drives that could benefit,
>> plus x86 is a different beast.
>
> When I mention OmniOS and SmartOS above, think the x86 port of Solaris.
> I ran into this problem using SATA disks in an HP Microserver (which
> would make a nice target market for the VMS x86 port, even if restricted
> to Intel CPUs, if that is a consideration).
>