Typical flash-based storage features and performance

Spoon wrote:
Patrick de Zeester wrote:

Spoon wrote:

We use IDE flash-based storage in our embedded systems. For several
years, our supplier has provided us with PQI DiskOnModules:

http://www.pqimemory.com/documents/domdata.pdf

I find their performance rather lacking.

Media transfer rate
write 1.2 MB/sec (typ.)
read 4.1 MB/sec (typ.)

Interface burst transfer rate
PIO mode 2 - 8.3 MB/sec (max)

In the past have used this particular DOM module. Not only the
transfer rate something to be desired, since it only supports PIO mode
transfers it also hogs the CPU, blocking the entire system while
reading and writing to disk.

There are also DOM modules from the same manufacturer which do support
higher transfer rates (quite a bit faster than yours, but still a lot
slower than a real hard disk) and supporting UDMA transfer modes which
reduces the CPU load quite a bit. These modules are not much more
expensive than the one you mentioned.

PQI's Industrial DOM web page is rather terse:
http://www.pqimemory.com/products-Domindustrial.asp

they do offer the aforementioned datasheet:
http://www.pqimemory.com/documents/domdata.pdf

Could you provide a link to one of the faster PQI DOMs?


http://www.pqi.com.tw/product2.asp?o...=175&PROID=306

Spoon wrote:
Patrick de Zeester wrote:

Spoon wrote:

We use IDE flash-based storage in our embedded systems. For several
years, our supplier has provided us with PQI DiskOnModules:

http://www.pqimemory.com/documents/domdata.pdf

I find their performance rather lacking.

Media transfer rate
write 1.2 MB/sec (typ.)
read 4.1 MB/sec (typ.)

Interface burst transfer rate
PIO mode 2 - 8.3 MB/sec (max)

In the past have used this particular DOM module. Not only the
transfer rate something to be desired, since it only supports PIO mode
transfers it also hogs the CPU, blocking the entire system while
reading and writing to disk.

This is my biggest fear.

Suppose the OS decides to write 4 KB at 1.2 MB/s (that's 3.4 ms).

The nightmare scenario is if the CPU can't do anything between two
16-bit transfers, with interrupts disabled.

Everything is put on hold for 3.4 ms... My real-time processes would be
quite unhappy.

How you system behaves depends on the OS and drivers I guess. With tests
we did on Windows XP embedded we found that the entire system could
freeze for more than 50 ms when the flash disk was exercised heavily.
This effect disappeared with an UDMA capable flash disk, and the CPU
load dropped from 100% to barely noticeable in that particular test.

There are also DOM modules from the same manufacturer which do support
higher transfer rates (quite a bit faster than yours, but still a lot
slower than a real hard disk) and supporting UDMA transfer modes which
reduces the CPU load quite a bit. These modules are not much more
expensive than the one you mentioned.

I will ask our supplier to provide one such DOM for testing purposes.

Regards.