Disk imaging strategy

Don Y · 2014-11-02T15:25:31+00:00

Hi, I'm writing a bit of code to image disk contents REGARDLESS OF THE FILESYSTEM(s) contained thereon. This doesn't have to be "ideal" (defined as "effortless", "minimal image size", etc.) but should be pretty close. It is not intended to be performed often -- "write once, read multiple" (i.e., RESTORE *far* more often than IMAGE). The challenge comes in the filesystem(s) neutral aspect. E.g., I should be able to image a disk containing FAT32, NTFS, FFSv1/2, QFS, individual RAID* volumes, little/BIG endian, etc. -- with the same executable! A naive approach to this would be to plumb dd to a compressor -- running both OUTSIDE the native OS. But, for large/dirty volumes, this gives you an unacceptably large resulting image -- because you end up having to store "discarded data" which could potentially be HUGE (consider a large volume that has seen lots of write/delete cycles) esp in comparison with the actual precious data! [I'd like to be able to store the image on a (set of) optical media and/or an unused "partition" somewhere] I.e., without knowledge of the specific filesystem(s) involved, you don't know how to recognize live data from deleted data. The *hack* that I am currently evaluating is to invoke a trivial executable UNDER THE NATIVE OS that simply creates large "blank" (i.e., highly compressible) files until the volume is "full", then unlinks them all. Doing this while the system is reasonably quiescent isn't guaranteed to "vacuum" all available space but would make a big dent in it (if the system is brought down shortly thereafter). [Yes, I understand privilege constraints in various OS's, quotas, etc. Those are all easy to work around...] Then, dd | compress (on bare iron). Again, not ideal but probably the best bang for the least buck?

Nov 02, 2014 103 Replies

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DecadentLinuxUserNumeroUno 11 years ago

On Sun, 23 Nov 2014 02:52:25 -0700, Don Y Gave us:

You're gonna want to see Mel Blanc's version of a gremlin.

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Dimiter_Popoff 11 years ago

That with the too many missing matches I would not take that lightly, mad as it may sound, you know. Gremlins or whatever, things do go missing sometimes in an inexplicable way for me, too - usually only to reappear at the location I initially looked for after minutes - sometimes hours - of search. Not very often but times enough to rule out being just in dreamland when looking there first. I just have no explanation about it but it does happen to me. May be not to everybody... Obviously even now if someone would tell me that even I would consider a mental issue but... it does happen to me.

Who knows, may be one day we'll discover that even "changing timeout values" can also go into that inexplicable category :D :D :D.

Just now I had another which wasted me an hour. I wish it were inexplicable but it was just Chinese.... Bought a multimeter from ebay to measure current consumptions of things, looked for an analog one which could do 1A at least; found one with 2.5A. Came with no 2.5A, just 0.25A max. OK, no time to deal with this, just put a negative ebay feedback and moved on. Used it at 250mA for the current thing (the one with the timeout values, it is a HV source). While messing with it(soldering live a 470uF at the incoming 12V past a tiny 10uH choke)the something died, consumption went way above

250mA. Unsoldered quite a few parts from the board to see what did die only to discover the deadman was the shunt resistor or something within the multimeter...... Consumption had not risen at all. I must have shorted the incoming 12V briefly - for a few tens of milliseconds - and the thing had died... They must have used 0402 resistors for the shunt :D (no time to investigate, just made an external one for 1A, back to work).

Dimiter

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Don Y 11 years ago

Well, when you *need* a match/light, it can quickly lead to PANIC!!

I've recently become distressed over having too many pairs of *shoes*! Seems like I can never find the pair that I am *supposed* to be wearing; always one of the pairs that I'm *not*!

Actually, L has been moving things when you're not looking; then, placing them back just AFTER you've searched a place! If you listen carefully, while you're running around "hunting", she's quietly giggling in the other room!

If you didn't notice at the time, it could have been milliseconds or

*weeks*! OTOH, when you *do* notice, it's within ohnoseconds!

Dunno. I've a couple of cheapie DVM's but rarely use them for measuring current (other than to verify charging current flowing into a battery, etc.). Always amazing how inexpensively they can make the things! There's a place, here, that frequently gives them away so you'll find people with 5 or 6 of the same make/model lying on in their shop and you KNOW where they got them! :-/

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