Re: Home made backup system
On Thu, 26 Dec 2019 09:51:59 -0500
rhkramer@gmail.com wrote:
> Again, I assume (I know what assume does) that "USB mass-storage
> device that acts like a hard drive" is (or might be) a pen drive type
> of device. I've had a lot of bad luck (well, more bad luck than I'd
> like) with that kind of device, and I suspect that the problem is
> more likely to occur when parts of the device are erased to allow
> something new to be written to it.
When I first started working with the technology behind what we now
call flash drives, back in the late Pliocene, their capacities were
measured in bits, and I think I worked with 256 bit and 512 bit
devices. At that time, you had to read several bytes worth, modify the
relevant bits, and write out the several bytes worth to make a change,
much like changing a sector on a floppy disk or hard drive.
As you conjectured, device life was measured in write cycles, usually
on the order of tens or hundreds of write cycles.
Today all of that is still more or less true, except the capacities
and lives of the devices are greatly extended.
And one other change: When I was working with these things, the host
computer's operating system device driver had to take care of all that,
including using different "sectors" to spread out the wear and avert
device failure. Today, all of that is "under the hood" of the flash
drive, completely invisible to the host computer.
This is similar to the evolution of the hard drive. Way back when five
megabytes was a lot of hard drive (I started working with the Seagate
ST-506), the operating system driver had to worry about encoding,
tracks, sectors, and heads, error correction, and about bad sectors and
re-mapping them. SCSI, and later, IDE, moved all that onto the drive
itself, and all the OS sees is a linear expanse of sectors.
So much of what you conjectured indeed goes on, but on the flash device,
and at a level utterly and completely invisible to the host operating
system. And it almost certainly does it better than most of us here
could do it.
--
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https://charlescurley.com
https://charlescurley.com/blog/
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