[Info-vax] more on minicopy

[Stephen Hoffman]

On 2013-01-02 19:38:29 +0000, Phillip Helbig---undress to reply said:

> In article <kc21k7$qq1$1 at dont-email.me>, Stephen Hoffman
> <seaohveh at hoffmanlabs.invalid> writes:
> 
>>> It seems to me that intentional dismounts of members of shadow sets are
>>> rare compared to unplanned node crashes
>> 
>> Shadowset members are being used for quick backups, and backups happen
>> rather more often than host crashes.
> 
> Hhmmm.  If the disk is quite active, then it might be difficult to get a
> consistent---only "crash consistent" copy from a shadow set.

Ayup.  Albeit involving a microscopically small (and sketchy) backup 
window, in comparison with the ginormous window involved with the 
traditional (and sketchy) online BACKUP mechanism.  Put another way, 
still ugly, but ugly for a much shorter window.

There are ways to freeze (some) running applications, either by 
grabbing the volume locks (poor, but workable), or by coding the app(s) 
to be backup friendly, or by a brute-force quick-restart.

But then this nub gets back to the hassles that are endemic with 
classic apps and the classic APIs.  It's fairly rare for applications 
(non-database applications) to implement on-line backup support, and 
VMS has no quescence mechanisms.  Which means that online backups and 
failovers get more "fun".

>  But if not much changes, there isn't as much need for a backup.

(Didn't we just have that discussion about system disks?)

> Of course, there are things in between, such as applications which do a 
> lot but can find a quiet point for a backup.  At home, though, I am in 
> one camp (stable
> disk, infrequent updates, mostly READ) or the other (active disk with  
> many open files).

OS X has integrated backups, which deals with the typical stuff for the 
typical operator.  These backups work very well on OS X clients and for 
typucal client file and data access patterns, and have also started 
working decently well for servers running the most recent releases.


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