Regarding the topic of speed of data recovery using GNU ddrescue, I use crappy
USB tri-head (ide and sata) interfaces to recover data from failing drives. I
can usually get about 12 MB/s top speed and can image a drive in a few hours
with that. Although I seldom do.
For example, the drive I am currently doing is a 120 gig 2.5 drive from a Mac.
It stopped being detected and the computer would not boot. It was replaced. I
got the failed drive to be recognized by patiently power cycling the drive
(unplugging and plugging the power cable) until it powered up properly and was
recognized. It only needs to get there once after which you don't unplug it
again.
I tried imaging the drive and got about 5 gigs over the first hour. I had to
reset it about a dozen times during this period
(unplug and replug the usb interface; hotplugging). It would shriek and click
before it would conk out, a cue that I would pick up on from about thirty feet
away. So I would know to drop what I was doing and restart the recovery.
After a few passes, I decided to try the much slower direct mode, which has
performed very well. It has been going for almost 14 hours now without any
more errors. I reckon the high ratio of error (115 gigs of error out of a 120
gig drive) is due to the high speed since I am reading the parts of the drive
that I wasn't able to read at regular speed (with no new errors). Although its
rate is currently only 368 Kb/s and if this keeps up, it will take until Friday
morning to complete, I don't care about the speed. Or rather, there's nothing
I can do about it.
As long as the drive is spitting out data, it's a success. Very few of my
customers are under a time crunch that requires the job be done in such a short
time anyway.
This phenomenon is not unique to this drive. I find that most of
the problematic drives I work on behave like this.
Would I get better rates in direct mode using a more sophisticated interface?
I dunno. But there are two show-stoppers that prevent me from exploring that
possibility.
The first is cost. I have fried a few components by plugging in my customer's
faulty hardware. Data recovery is usually "no data - no charge". So there's
no way that I am risking more than a few dollars worth of equipment on
questionable hard drives, especially faced with the possibility that these
cases are hopeless and therefore I won't get paid.
USB Tri-Head adapters cost less than ten dollars each, including the power
supply.
The other problem is the eSATA interface. On the machines on which I have
tried an eSATA interface, the problem is that they are not hot-swappable like
USB devices. In one case, the drive is not recognized unless it is present at
boot
time. Since I often need to power cycle the drive several times to get it to
"come alive", I would need to reboot the computer each time I power cycle it to
get the bios to check to see if it can recognize the drive (the motherboard
needs to see it before the kernel can assign a /dev to it.) Annoying.
In another case, the only way to reset the drive was to hit the power button,
which would cause the drive to reboot and in many cases, once you get the drive
to "come alive" you never want to power it down. A USB interface can be
plugged and unplugged without powering off the drive.
So, is there an sSata interface out there that can cycle the eSata interface
without powering off and on the drive?
So, I'm all for high speed, but not at the cost of leaving data behind.
Cheers!
Andrew Zajac
AndrewZajac.ca
ubuntu-rescue-remix.org
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