[OpenAFS-devel] Re: [OpenAFS] Re: 1.6 and post-1.6 OpenAFS branch management and schedule

[Jeffrey Hutzelman]

--On Thursday, June 17, 2010 04:12:48 PM -0500 Andrew Deason 
<adeason@sinenomine.net> wrote:

> On Thu, 17 Jun 2010 15:54:25 -0500
> Andrew Deason <adeason@sinenomine.net> wrote:
>
>> And as has been mentioned elsewhere in the thread, you need to wait for
>> the VG hierarchy summary scan to complete, no matter how fast salvaging
>> is or how many you do in parallel. That involves reading the headers of
>> all volumes on the partition, so it's not fast (but it is very fast if
>> you're comparing it to the recovery time of a 1.4 unclean shutdown)
>
> Also, while I keep talking about this, what I haven't mentioned is that
> it may be solvable. Although I've never seen any code or even a
> complete plan for it yet, recording the VG hierarchy information on disk
> would obviate the need for this scan. Doing this would allow you to
> salvage essentially instantly in most cases, so you might be able to
> recover from an unclean shutdown and salvage 100s of volumes in a few
> seconds.

It's also worth noting that in a namei fileserver, each VG is actually 
wholly self-contained, so there is no reason in the world why you should 
have to scan every VG on the partition before you can start salvaging any 
of them.  The salvage server design really should take this property into 
account, as it seems likely that some future backends may also have this 
property.

-- Jeff