[Info-vax] free blocks

[Stephen Hoffman]

On 2013-01-02 18:35:51 +0000, Johnny Billquist said:

> On 2013-01-02 16:00, Bob Koehler wrote:
>> In article <kbeubt$11e$1 at news.albasani.net>, Jan-Erik Soderholm 
>> <jan-erik.soderholm at telia.com> writes:
>>> 
>>> And, this was/is not done dynamicaly, as far as I know. You had/have to run
>>> a specific tool to check this (ANALYZE /MEDIA <dev>).
>> 
>> Nope.  You used anal/media to initialize the bad block file.  Bad
>> blocks discovered while the disk was in use were added to the bad
>> block file.
>> 
>> When VMS sees a bad block on write, it marks the block bad and writes
>> the data on a different block, and nevre uses that block again
>> (unless a tool like anal/media removes the mark).
>> 
>> When VMS sees a bad block on read, it marks the block bad and does the
>> best it can to read the data.  Each attempt to read will log I/O errors
>> on the device.  Deleting the file which contains the bad block will
>> cause the block not to be used again.  The application reading the
>> file will see I/O errors also, if it looks.
>> 
>> VMS doesn't need smarts to deal with revectoring disks differently.
>> VMS just never sees bad blocks reported from the hardware.
> 
> That depends on the disk and controller.
> On an UDA-50, VMS have to do the revectoring of bad blocks. So bad 
> blocks are reported to VMS. However, VMS do not use BADBLK.SYS to 
> record them,

AFAIK, BADBLK.SYS is still used.  That's where the blocks with 
uncorrectable read errors are "stored", pending eventual revectoring.

> but instead initiates a bad block replacement operation, trying to 
> recover the data from the block, allocate a replacement block, and 
> wrote the recovered data in that block, and finally revector the old 
> bad block so that it never is seen as bad again.

Once the write to the bad sector or the file delete happens, yes.

> After that, VMS don't have to worry about the bad block, the 
> replacement block is automatically used by the controller and disk.

AFAIK, the OpenVMS IDE implementation doesn't support revectoring, 
which is why DQ disks get kicked out of the HBVS VU on read or write 
errors.



-- 
Pure Personal Opinion | HoffmanLabs LLC