[Info-vax] Uptime for OpenVMS

[Johnny Billquist]

On 2011-05-13 13.43, Bob Eager wrote:
> On Fri, 13 May 2011 11:18:10 -0600, Johnny Billquist wrote:
>
>> On 2011-05-13 09.38, Steve Thompson wrote:
>>> On Fri, 13 May 2011, Bob Eager wrote:
>>>
>>>> On Fri, 13 May 2011 01:49:24 -0600, Johnny Billquist wrote:
>>>>
>>>>> Ok. True. Yes, if the inode numbers were preserved, then it would be
>>>>> theoretically possible.
>>>>> However, the OS have no way of knowing for sure that the inode
>>>>> numbers were preserved, so that is more on the theoretical side (I
>>>>> actually don't know of any way to actually preserve inode numbers
>>>>> when copying a disk...).
>>>>
>>>> The equivalent of BACKUP/PHYSICAL would do it. It would be nice
>>>> though...
>>>
>>> That would be dd.
>>
>> Hmm. Yuck! Yes, dd would be a way to copy a disk preserving the inode
>> numbers. Output disk must be the same size as input disk. And it will be
>> slow. But ok... :-)
>
> Don't see why it has to be slow. Give it a nice big buffer and it can be
> very fast.

You're still copying a lot of disk blocks (I would suspect) that are 
actually not in use. A copy operation that understands the disk content 
needs to copy much less. But big buffers will undeniably improve 
performance significantly. I don't even dare to think how slow dd is 
when you use 512 byte buffers... :-)

>> But the OS would still not know that this new disk was equivalent to the
>> old one...
>
> Yes, that *is* the problem.

Yeah.

	Johnny