On 2010-06-06, Michael A. Terrell wrote:
Wes wrote:
"Michael A. Terrell" wrote:
There is no moving mechanical mass in a solid state drive so it's a
lot faster that conventional drives. there is no oxide to shed from the
spinning media, and they don't mind vibration or suffer from mechanical
shock like older drives.
But the flash cells have a finite life as in write cycles.
It was well over 100,000 write cycles the last time i worked with
solid state drives. Since the drive in a machine tool is mostly a read
device, it should outlast the tool. NASA had no problem with the
expected life span in 2000.
It depends on the OS. Unix variants (unless the filesystem is
mounted read-only) update the last-accessed time in the inode for each
file every time you read it. And there are a number of file inodes
sharing the same 512 byte block, so the number of write cycles in an
active directory would accumulate rather faster than you might expect.
This could at least be a problem with EMC (which is linux based)
-- unless care is taken to mount the SS drive read-only, and keep some
other form of medium for read-write. Perhaps set it up using the SS
disk something like a liveCD, and copying it into a RAM-DISK for normal
execution, and only remounting it read-write when you absolutely need to
write something to it.
With the Microsoft FAT filesystem, I don't think that there is
any equivalent last-accessed time, but I don't know what other gotchas
might be present.
Would you rather use a solid state drive in a machine, or look for a
used mechanical IDE/PATA drive that might still work while the machine
is down, and nothing is being shipped? Some interfaces won't work with
the newer drives, because the block size is too large on 300 GB and up
hard drives. from what I've heard, there are no new IDE/PATA drives
being built, and what is for sale is the last in the pipeline.
Making me happy to use SCSI and FC disks. :-) At least Sun
doesn't seem to have any hardware-set limits on those. :-)
Sophisticated wear leveling algorithms try to keep the wear spread across the cells.
That can help -- somewhat.
The technology is improving but it isn't at a price point to drop spinning metal platters
yet. My pile of drives that have failed or were recovered and no longer trusted is
getting pretty darn big.
It will continue to grow, because the higher the density, the easier
it is to corrupt.
:-)
Then there is the issue that a CDROM or DVDROM doesn't have an archival lifespan. I fear
a whole lot of digital content is going to die faster that content produced only 50 years
ago. 1980-2030, the lost decades.
Critical data should be refreshed every five years to new media, just
to be safe.
Yes -- now all you need is the time to keep a growing stack of
CD-ROM and DVD-ROM safety copies up to date. :-)
Enjoy,
DoN.
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