Solid State (Flash) Drives

  • Thread starter Michael Griffin
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Michael Griffin

I have several applications where I would like to improve the reliability of some existing computerised test equipment. One of the less reliable parts of a computer is the hard drive. I am considering using solid state (flash) disk
drives instead of conventional rotating disks. There are available from a number of sources ATA/IDE flash disks in sizes from 8 mega-bytes up to 900 mega-bytes. These devices are intended to interface to an IDE controller in the same way as a conventional drive, and even have the same form factor and mounting holes.

My application software (in use for several years) uses a DOS operating system. The software logs test results in a series of ASCII files, with new log files being started several times per day. There are no other files which are repeatedly written to or erased (excluding the DOS directory structure), and a moderately sized drive should hold several months worth of data before the older data is erased. One drive would hold the application, DOS, and all data files.

I was initially skeptical about whether this was feasible, but upon looking into the subject I discovered that with current flash write endurance and wear leveling techniques, the drives would appear to be able to last for several decades in this application. "Wear levelling" has a very strong effect on this calculation as only a very small percentage of the drive capacilty is written to per day.

My questions are:
1) Has anyone else used these drives in a similar (or any) application and,
2) do they have any comments they would like to share?
3) Is any OEM's particular wear leveling technique best (or worst) for this application?

I understand that using Windows would raise serious problems due to the swap file, but I am dealing with DOS, which doesn't have this problem.

Michael Griffin
London, Ont. Canada

Sounds like we're doing similar things.
I use 8 to 16 meg Compact Flash Cards to hold ASCII data from my Rugid PLC "": .
The only problem I've experienced is formatting these units with FAT12. Microsoft, in their infinite wisdom, employs different FAT12 methods of formatting disks <16 meg (actually 16 meg less one byte) in ALL their OS's.
I've discovered that cards (<16 meg) formatted with one OS often aren't readable in other OS's.

I'm not sure this problem exists with cards >16 meg, after which MS switches to FAT32.

If you'd like to continue this discussion off-line, drop me a note.

Mark Hill

Alex Pavloff

I've been playing with CompactFlash disks recently, and the main things that I've noticed is that different BIOSes with different settings for large-disk-access can cause problems when put in different machines. This seems odd, because I don't even have a large disk (16 meg compact flash), but I find the entire system to work if you make sure that you have all IDE interfaces the disks are plugged into are set as "NORMAL". LBA, LARGE, EXTRA LARGE, EXTRA EXTRA LARGE WITH MUSHROOMS seem to be erratic.

Alex Pavloff
Software Engineer
Eason Technology
I would suggest using compact flash. I think that you can get drives that are DOS compatible, as they said to be pin for pin compatible with IDE. You can buy high capacity CF cards easily and they are even easier to replace. (or steal..., hmm maybe not such a good idea afterall)

Just an idea,

Bill Sturm

Donald Pittendrigh

Hi All

Might be easier to use a USB drive, I have been very happy with my 128Mb drive which although bought for different purposes to yours, will offer the same features as a flash drive. There is only a problem transporting between operating
systems if disk compression is used, for example I use mostly Win2000 and having switched compression on during formatting, the drive is not visible to Win 98. Uncompressed no problem, and it can be used for booting, I have tried with Win2000 and it works, haven't tried with the others.

Donald Pittendrigh

James Ingraham

With standard ATA Flash PC Cards we've had perfornamce issues that are so bad it can occaissionaly corrupt data. I would recommend a higher performance Flash drive, such as those from BiTMICRO Networks ("": ).

-James Ingraham
Sage Automation, Inc.

Michael Griffin

I am looking at something similar to this drive. I wasn't considering the memory "card" style. There are a number of devices on the market which are intended as direct hard drive substitutes.
You have a good point about checking the performance though. Since I am dealing with DOS, the write times have to be comparable to (or better than) a conventional hard drive in order to not affect test cycle time. The system
has to log a small data record at the end of every test (we also erase old data regularly). The memory corruption problems you had may have been due to feeding the "card" data faster than it could handle it.

"Thank you" to the others who also replied on this issue. The points which were raised about 12 bit FAT formats are particularly interesting. However, since I am planning on using a larger drive (I'm not quite sure large) I
won't run into this.
The endurance of the flash depends upon using a large enough drive for the "wear leveling" system to work on to spread the write operations out. If only a small proportion of the drive is written to daily, then the drive will last a large number of days (decades even). If you use an operating system which has predictable disk access characteristics, you can calculate this life. I suspect that some "wear leveling" systems may be better suited to this application than others. I have some more research to do on this.

Michael Griffin
London, Ont. Canada