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

[Paul Sture]

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.

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).

-- 
The optimist believes we're living in the best of all possible worlds
and the pessimist is afraid that's true.