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#11
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check or scan _without_ retesting sectors?
Bill Blanton wrote in
g.com: I doubt it too. Windows would probably stop DOS6.2 in its tracks. As far as running the 98 version,, even if you could get it to run, I wouldn't trust it. It doesn't use the Windows API, and has no concept of "open" files in that environment. That's true too, but there is technically a possibility that something could use. As a disk controller can only access one byte (bit?) at a time, the OS has to wait no matter how multitasking it is, and if that wait method can be held up for an instant, the tool doing that could read, write inverse of what it saw, test with new read, write back original value, retest, and move on, allowing other things to access that space. In which case it may be possible for a tool like this to avoid locking large spaces and manage not to interfere other than appear to be a cause of small delays, from the perspective of anything else. Spinrite might have managed it, but that too was meant to run only in DOS, and I don't know if it did the sector marking and unmarking. But it might be a better tool than Scandisk for repeated surface testing. BUT, I can't remember if it will even touch a floppy disk..... PS. I found a DOS 6 Scandisk, and it does balk. Maybe messing with some version fix could do it but that was something I never did figure out how to use, and I doubt that this scanning will be usefully done in Windows anyway. |
#12
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check or scan _without_ retesting sectors?
On Sat, 19 Nov 2011 08:56:28 +0000, "J. P. Gilliver (John)"
put finger to keyboard and composed: I have come across a utility (I forget the name) that repeatedly reads (or attempts to), I think possibly by unorthodox instructions to the disc controller, for hours on end - mainly for last-ditch recovery attempts, I think. I think it was OS-independent - possibly booted from a floppy; it is quite expensive. You're probably thinking of SpinRite or HDD Regenerator. I would recommend that you avoid them. Both are considered by the data recovery profession to be potential drive killers. In fact many (most?) of Steve Gibson's claims no longer apply to drives made within the last 20 years. Just look at the screenshots on the web site. The most recent example is for a 200MB drive (yes, that's megabytes, not gigabytes). The reason that SpinRite may be dangerous is that it is invoked by desperate users in a vain attempt to extract data from bad sectors. Modern drives often suffer from weak heads due to "thermal asperities". SpinRite repeatedly hammers away at a bad sector, perhaps several thousand times, hoping for one good read. This potentially accelerates the failure of weak heads. In any case, even after successfully extracting the data, these data are written back to the source drive rather than to a backup. A much better approach to data recovery is to clone the drive, sector by sector, using a utility that understands how to work around bad media. Two examples are ddrescue and dd_rescue, both freeware. Ddrescue keeps a log file, so you can resume after an interruption. It also allows you to image the drive in reverse, effectively disabling cache. A good standalone DOS utility that can perform a surface scan on your drive is MHDD. It will identify "slow" blocks, ie those that require several read retries. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#13
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check or scan _without_ retesting sectors?
Lostgallifreyan wrote:
Bill Blanton wrote in g.com: I doubt it too. Windows would probably stop DOS6.2 in its tracks. As far as running the 98 version,, even if you could get it to run, I wouldn't trust it. It doesn't use the Windows API, and has no concept of "open" files in that environment. That's true too, but there is technically a possibility that something could use. But would you really be willing to risk it, given what Bill said? Nothing like playing with fire, lol. I think I'd pass on this one. :-) |
#14
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check or scan _without_ retesting sectors?
"Bill in Co" wrote in
m: Lostgallifreyan wrote: Bill Blanton wrote in g.com: I doubt it too. Windows would probably stop DOS6.2 in its tracks. As far as running the 98 version,, even if you could get it to run, I wouldn't trust it. It doesn't use the Windows API, and has no concept of "open" files in that environment. That's true too, but there is technically a possibility that something could use. But would you really be willing to risk it, given what Bill said? Nothing like playing with fire, lol. I think I'd pass on this one. :-) Well, I would, but the real question is: would anyone who hasn't got a redundant copy risk it? I was looking at ddrescue just now (Franc Zabkar's suggestion), and even that can't work magic. However we slice it, once something breaks down, even then two compies that broke down might be better than one, if they break in different ways. (ddrescue might find bad blocks in different places, but enough good ones to get a complete image from two or more decaying CD's or floppies, for example...) So whatever we do, a copy in advance is best, for every reason we can throw at it. Even when things are great all round, it lets people like me say 'yes' to your question. I was going to suggest clonign a disk as Franc said, btu all I could think of was Ghost, which isn't free, and maybe isn't all that good for all I know. ddrescue is at 1.12 in a Win32 version that needs cygwin, and you have to access devices as WD0 or whatever. (WDn is a BSD naming, but it's the same idea, Unix style device names and paths...) I also saw a forceful recommendation for this: http://www.datarescue.com/photorescue/v3/drdd.htm ....but I have no situation that can let me judge how good it is when it really matters. |
#15
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check or scan _without_ retesting sectors?
In message ,
Lostgallifreyan writes: [] That's true too, but there is technically a possibility that something could use. As a disk controller can only access one byte (bit?) at a time, the OS has to wait no matter how multitasking it is, and if that wait method can be held up for an instant, the tool doing that could read, write inverse of what it saw, test with new read, write back original value, retest, and move on, allowing other things to access that space. In which case it may be possible for a tool like this to avoid locking large spaces and manage not to interfere other than appear to be a cause of small delays, from the perspective of anything else. Just for curiosity: letting the W95 GUI scandisk run (on my dodgy floppies) makes the machine almost grind to a halt when trying to do anything else), not just cause small delays; to the extent that keystrokes or mouse clicks take tens of seconds to have effect. (The mouse cursor does move OK.) [] -- J. P. Gilliver. UMRA: 1960/1985 MB++G.5AL-IS-P--Ch++(p)Ar@T0H+Sh0!:`)DNAf "Bother," said Pooh, as Windows crashed for the umpteenth time. |
#16
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check or scan _without_ retesting sectors?
Lostgallifreyan wrote in
: I was going to suggest clonign a disk as Franc said, btu all I could think of was Ghost, which isn't free, and maybe isn't all that good for all I know. I must qualify that.... Ghost is great, if the disk is good. I wpuldn't use Acronis or anythign else because I stayed with Ghost, it never disappointed me except one or two versions which I avoid. What I meant was that if there is disk trouble, I don't know if it works. It WILL do a forensic bit-copy, but whether it will attempt with different block sizes or do anythign other than either hammer at it crudely, or balk and give up first time, I don't know. I've seen some fairly sophisticated error reporets from Ghost at times, but each time it went over my head, and balked anyway. And sometimes it just worked next time anyway. Probably better to use a tool that makes it a LOT clearer what its up to, and what it finds, if you need bad-read recovery and not just exact imaging of known good disks. |
#17
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check or scan _without_ retesting sectors?
In message , Franc Zabkar
writes: On Sat, 19 Nov 2011 08:56:28 +0000, "J. P. Gilliver (John)" put finger to keyboard and composed: I have come across a utility (I forget the name) that repeatedly reads (or attempts to), I think possibly by unorthodox instructions to the disc controller, for hours on end - mainly for last-ditch recovery attempts, I think. I think it was OS-independent - possibly booted from a floppy; it is quite expensive. You're probably thinking of SpinRite or HDD Regenerator. I would Yes, I think it was SpinRite. recommend that you avoid them. Both are considered by the data recovery profession to be potential drive killers. In fact many (most?) of Steve Gibson's claims no longer apply to drives made within the last 20 years. Just look at the screenshots on the web site. The most recent example is for a 200MB drive (yes, that's megabytes, not gigabytes). I saw it being used on the drive from a DOS ('286-based, IIRR) machine. I'm pretty sure it was a lot less than 200M. The reason that SpinRite may be dangerous is that it is invoked by desperate users in a vain attempt to extract data from bad sectors. Modern drives often suffer from weak heads due to "thermal asperities". SpinRite repeatedly hammers away at a bad sector, perhaps several thousand times, hoping for one good read. This potentially accelerates the failure of weak heads. In any case, even after successfully extracting the data, these data are written back to the source drive rather than to a backup. I was trying to remember where the rescued data was being put. A much better approach to data recovery is to clone the drive, sector by sector, using a utility that understands how to work around bad media. Two examples are ddrescue and dd_rescue, both freeware. How do they handle bad sectors though? Just give them a default value? Ddrescue keeps a log file, so you can resume after an interruption. It also allows you to image the drive in reverse, effectively disabling cache. A good standalone DOS utility that can perform a surface scan on your drive is MHDD. It will identify "slow" blocks, ie those that require several read retries. How many retries is too many though? I _think_ SpinRite (or whatever it was) had a settable maximum, though that could be disabled. - Franc Zabkar -- J. P. Gilliver. UMRA: 1960/1985 MB++G.5AL-IS-P--Ch++(p)Ar@T0H+Sh0!:`)DNAf "Bother," said Pooh, as Windows crashed for the umpteenth time. |
#18
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check or scan _without_ retesting sectors?
"J. P. Gilliver (John)" wrote in
: Just for curiosity: letting the W95 GUI scandisk run (on my dodgy floppies) makes the machine almost grind to a halt when trying to do anything else), not just cause small delays; to the extent that keystrokes or mouse clicks take tens of seconds to have effect. (The mouse cursor does move OK.) Good point. Maybe I underestimated the effects of my wheeze. So it really does look like staying with DOS. I pointed out a Windows tool just now in another post, so maybe the same thing applies. I notices that in protected mode good data seems to copy MUCH faster than in DOS. I still don't know enough to know exactly why, but I suspect that if anything causes slow reading of data, you might as well do it in DOS so you have safe direct hardware access. |
#19
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check or scan _without_ retesting sectors?
"J. P. Gilliver (John)" wrote in
: A much better approach to data recovery is to clone the drive, sector by sector, using a utility that understands how to work around bad media. Two examples are ddrescue and dd_rescue, both freeware. How do they handle bad sectors though? Just give them a default value? From what I could see, a log file lists locations and the copy may have some arbitrary value, whatever was already in that space. So long as the log file maps what is knowm to be recovered, it also knows what is not, so it's not relying on whatever is in the unwritten area of the copy. I don't think they fix the disk or mark bad sectors (if so, I missed that), I think they just copy areas that look good, like doing the easy chunks of a jigsaw first, and map out a pattern indicating what is not yet done. Ideally, I think they never write to the source disk at all. |
#20
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check or scan _without_ retesting sectors?
In message ,
Lostgallifreyan writes: [] I notices that in protected mode good data seems to copy MUCH faster than in DOS. I still don't know enough to know exactly why, but I suspect that if anything causes slow reading of data, you might as well do it in DOS so you have safe direct hardware access. I can't remember what protected mode means, but I vaguely do remember some copying going faster - I think it was floppy to floppy on the same drive (remember "insert source disc"/"insert destination disc"?), where I assumed it had a much bigger buffer in the more advanced mode. -- J. P. Gilliver. UMRA: 1960/1985 MB++G.5AL-IS-P--Ch++(p)Ar@T0H+Sh0!:`)DNAf "Bother," said Pooh, as Windows crashed for the umpteenth time. |
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