Defragmenting Memory card

[wyrm]

In the case of a stream, it's always the next block. In the case of fragmented data, there is a pointer somewhere (either at the end of that block, or in a address table, fat, i guess), which needs to be referred and the destination calculated. This is what i think takes more time.

This makes sense, but i dont think that it would make a big difference on performance unless you are using a very slow processor. Most time is spent waiting for I/O to finish, not on the logic to find the next block. There is also a FAT size impact to consider, more fragments leads to a bigger FAT, and consequently uses more RAM and spend more time on writing the FAT to the card (write access is very slow). But even considering these, its not worth to defrag flash disks, they have a limited amount of erase cycles, and every time you defrag it you will drastically shorten the card's life.

Also, "next block" is relative. As i said before, flash drive do wear levelling, so, what you think is contiguous in fact isn't. There is an internal controller on the card, which will spread the data evenly across blocks. You can write to a given block and it will be stored on a memory cell, you write to the same block again, and it will be stored on different memory cell. What you see as contiguous on your OS is in fact spread "randomly" on the card.

This should help.

Should I defrag my memory cards? - MobileRead Forums

How do I defragment my Pocket PC memory cards? Do I need this at all? | Smartphone & Pocket PC magazine

Werner Ruotsalainen dont know what he's talking about.

Some better reference is:
http://www.sandisk.com/Assets/File/O...rLevelv1.0.pdf
(interesting so you can calculate how much card lifetime you would lose by defragging your card every month like Werner suggests or by using it as swap memory). Note that 2M erase cycles are valid for original I-grade sandisk SDs, for generic branch SDs this can be as low as 10k erase cycles. Also note that swap will write to the disk at very high rates (much more (>100X) than the worst case scenario by sandisk).

[sushjames]

@wyrm : Wow too technical for me, anyway thanks for the great information.. At last i'm learning something new

[swifty]

there is always a fitting quote somwhere:

<richard> To be fair to windows, there is one thing you can do on it that you can't do on Unix
<teifion> Can you do it on my Mac?
<richard> No, it is unique to Windows
<teifion> What is it?
<richard> You can defrag stuff

QDB: Quote #707810