[Info-vax] backup /image on Windows or Unix?

[Stephen Hoffman]

On 2013-01-23 13:27:15 +0000, Dirk Munk said:

> One of the nicest features of VMS is backup/image. Take a badly 
> fragmented disk as input, and you will get a beautiful structured disk 
> as output, all files contiguous etc.
> 
> I have always been looking for utilities that can do the same in 
> Windows and Unix, but I never found them.
> 
> Does any one in this group know such utilities?

Nope.  Well, with OS X, operating system reinstallation is easy, and 
asr and Disk Utility and such can be used for this task.

Defragging was useful when you were cramming too much data onto 
too-tiny disks and into too little physical memory, and when 
applications were more commonly doing incremental writes and not simply 
reading in and writing out whole files.   SSDs and hybrid drives also 
mean that disk seeks aren't a factor.

Here's an (old, retired) write-up from Apple on this topic for OS X 
<http://support.apple.com/kb/HT1375>.  OS X also does automatic 
defragmentation and automatic hot file optimizations, and (with the 
Fusion hybrid SSD-HDD drives) relocates the active files into the 
fastest available storage, and less active files onto slower HDD 
storage.   I'd be surprised if Linux weren't doing the same sorts of 
optimizations, or working on adding them, too.

VMS can unfortunately default to near-pessimal I/O patterns here, with 
it's fondness for reading and writing dinky records, and the default 
fondness for hitting the disk rather than caching the updates in 
memory.  This tends to push most of the optimizations into the 
application and out into the controllers and controller caches, where 
those capabilities are available.  There's also no OS-level hot-file 
processing, short of DFU or DFO.  (VMS did recently acquire support for 
some SSDs, which can help.)  Applications can have their RMS defaults 
tweaked which can help, and folks updating VMS applications do have 
some choices, but these tend to require explicit coding.  Which means 
you can sometimes need to deal with fragmentation.  (Then there's the 
"fun" of defragmenting within an RMS file...)

Put another way, Don't assume that solutions from older platforms are 
applicable to newer platforms.  Look at the performance limits and the 
problem(s) you're having with your particular operating system(s) and 
current applications.  See if you even have a problem, and whether a 
targeted defrag might be appropriate.   If some sort of defragmentation 
is even necessary.   How often are most VMS boxes using their swap 
files these days?

In time, I'd expect to see the whole of the baroque hard disk drive 
interfaces we're using — SATA, SAS — increasingly deprecated, with 
larger swaths of non-volatile memory becoming common.  That'll mean 
changes to the northbridges or SOCs and to the applications, or maybe 
PCIe-based non-volatile storage and some drivers, but it'll provide a 
saner API for new and updated applications than what we're now using.

But then this is a VMS group and not one particularly known to be 
familiar with Windows or Linux or...  Might want to try your generic 
"defragmentation?" question elsewhere, and see if you get different 
opinions or recommentations or tools.


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