SparkFun Forums

[UhClem]

This would also mean that the 250 kB/s you derived in previous post would therefore represent the maximum throughput of a system (with10MHz SPI) capable of dealing with fragmented drives?

That depends on what your code does. Plus remember that I ignored all the command overhead and card sector write times. That will cut into the maximum.

If you are writing to a fragmented file system you could end up having to scan a lot of the FAT in order to find the next free cluster.

As an example consider what happens if you run into a 10MB file that you have to skip over. On a card with 8K clusters that is 1280 clusters or 5 sectors. In this instance worst case is 6 sector reads and 2 sector writes to allocate a new cluster. Plus all the time spent scanning the sectors. If you don't have sufficient data buffers to cover for this delay then you will drop data.

[jairomacon]

SD cards are known as the non-volatile memory card.most SD cards ship Pre-formatted with the FAT or FAT 32 file system on top of an MBR partition scheme. The ubiquity of this file system allows the card to be accessed on virtually any host device with an SD reader.There are some classes defined to their bit rate speed:
Class 2: 16 Mbit/s (2 MByte/s),Class 4: 32 Mbit/s (4 MByte/s),Class 6: 48 Mbit/s (6 MByte/s), Class 10: 80 Mbit/s (10 MByte/s) ETC.
The higher Bit rate is more useful to you for such project. else there is no specified company to create high rates SD card.
For the FAT16 file system & SD cards Although the De-fragmentation is more useful to get the high speed rate.

[UhClem]

SD cards are known as the non-volatile memory card.most SD cards ship Pre-formatted with the FAT or FAT 32 file system on top of an MBR partition scheme. The ubiquity of this file system allows the card to be accessed on virtually any host device with an SD reader.There are some classes defined to their bit rate speed:
Class 2: 16 Mbit/s (2 MByte/s),Class 4: 32 Mbit/s (4 MByte/s),Class 6: 48 Mbit/s (6 MByte/s), Class 10: 80 Mbit/s (10 MByte/s) ETC.
The higher Bit rate is more useful to you for such project. else there is no specified company to create high rates SD card.
For the FAT16 file system & SD cards Although the De-fragmentation is more useful to get the high speed rate.

Interesting tidbit I just noticed in the SD 2.0 spec:

7.2.15 Speed Class Specification
As opposed to SD mode, the card cannot guarantee its Speed Class. In SPI mode, host shall treat the
card as Class 0 no matter what Class is indicated in SD Status.