Write Speed on High Capacity SD Cards as They Fill Up

I recently purchased my first 8 GB Sandisk Extreme III SD card. After I

purchased it, someone told me that as the card fills up, the write speed becomes

noticeably slower. More than likely I will download my photos to a computer

long before I fill the 8 GB card. The price (from Adorama with a Sandisk

rebate) was so low I couldn't resist.

 

My question is, has anybody who has an 8 GB card found this to be true? I did a

search here but didn't find anything on the topic.

 

I've read all of the logic for buying several smaller capacity cards, that's not

the issue here.

I have a D80.

I only have a couple of 8G Compact Flash (CF) memory cards, not SD. At least I have never heard of this issue before, and I see no reason why the write speed would slow down as a card gets filled.

 

At least among Nikon DSLRs that use SD cards, they all max out at 3 frames/second or slower. Therefore, a card's write speed should hardly be an issue.

 

On a D3 or D300 that goes up to 9 or 8 frames/second, the camera would empty the buffer a bit faster if you use an Extreme IV for Lexar 300x card that is UDMA compatible. I have actually tested that although it is somewhat academic in real-life shooting. For SD card based cameras, I wouldn't worry about that at all.

 

P.S. One of the main Extreme memory card designers at Sandisk happens to be my classmate from graduate school some 20 years ago. I might ask him next time I see him.

The access speeds of nand flash is fairly constant, with sequential access being faster than random. Hard drives tend to slow down when getting filled, but that is due to file fragmentation that tends to occur, which is purely a software problem. On camera memory cards, fragmentation shouldn't be an issue in normal usage.

 

So in short: I can't come up with any reason for the statement to be true.

I recently got a Transcend, Class 6, SDHC card. Combined with a Sandisk Extreme USB reader (yes they do work with SDHC cards), I tested it with HD Tach and got a consistent 19 Mb/sec transfer rate across the entire card.

Diane, are you trying to say you didnt find that happening in D80?

 

:-)

Thank you everyone for your replies. I feel a little better now.

 

Arun, I just got the card and haven't even had a chance to use it yet. And I didn't want to run through 400 actuations just to see if it was going to slow down. After someone told me that it will eventually slow down, I wanted to hear what everyone on the forum had to say. It was information I had heard second hand, so I wanted to know more about it.

Bruce, Sandisk supplied a very small Sandisk reader (it's really cute) with the 8 GB card, but it only works on SD cards.

They're not only cute, they work very well according to a site that recently reviewed a load of card readers.

 

Sandisk doesn't indicate on their site that the Extreme III card reader works with SDHC cards. Since I use SD and CF cards I've used that reader for over a year and didn't realize that it also worked with SDHC cards.

Let me expand a little bit on Oskar's idea. Fragmentation is always an issue and affects write speed for a hard drive as is fills. It won't affect a memory card like SD or Compact Flash unless the user has a habit of reviewing and deleting photos files IN-CAMERA. Creating holes in the sequential storage by deleting photos intermittently among the files on a card will force the write system to deal with fragmentation. I can't say I've observed this myself, but my suspicion is that the camera's write system probably won't deal with it as well as computer hard drive. SO it seems to me there could be slow-down under those circumstances.

It's good that you got an 8GB so there will be less compelling need to delete a lot while shooting. Besides making the card work harder to read/write data (thus logically slowing down the action), fragmentation scatters bits and pieces of image data across the surface of the card, thus making it next to impossible to salvage the images intact when a card goes bad.

 

Practically all I use now are 8GB cards and they are filled to over 90% of capacity most of the time. There were times when the camera would not shut down when in the midst of transferrring data from buffer to card, but I haven't experienced a problem bad enough to become an issue, except, perhaps, a slight delay right after a stretch of continuous frames.

 

Hope this helps,

Mary

I don't think that deleting a couple of photos amount to fragmentation that is a problem and you should be able to delete from the end without things getting fragmented. On a computer, a lot of files are written, deleted, extended and truncated and it takes a while before fragmentation becomes an issue. Of course, problems should be avoided, one shouldn't worry too much either.

See this the following statement in an article by Rob Galbraith regarding new SSD for computers, which also applies in general to other flash memory, including CF cards:

 

http://www.robgalbraith.com/bins/content_page.asp?cid=7-9309-9384

 

Note the statement:

 

"What you'll see is that the Crucial 32GB SSD writes fast and reads even faster, that it doesn't slow down much at all when it's full and that to take advantage of its speed you'll need to deploy the SSD in a configuration that's up for the job. "

Oskar is right, there is no need to be paranoid about fragmentation as long as one does not habitually use deletion as an alternate method to find space. I had attempted to recover a bad SD card for a colleague and found the images to be serverely fragmented. It was not a large card, so she apparently kept deleting and filling it.

 

Mary