rehess Loc: South Bend, Indiana, USA

What "changes" is credibility; someone who cannot select the right cognate may be wobbly on other details also.

BHC Loc: Strawberry Valley, JF, USA

Returning to the original issue, fragmentation is one of those little annoyances that occurs on Win systems. It is neither right nor wrong, just another way of maximizing disk usage (albeit at the possible loss of a little speed). I defrag my Win computers every month because I do not use them often; I do it at night (scheduled) and never have any problems. It should be noted that defrag software does not do a perfect job, and that repeat defragmentation accomplishes nothing. Bill Gates didn't make all that money making a software package designed to clog up; I just wish he (and Tim Cook) would spend a bit more on the quality of their respective GUI's.

Those that say a Mac never needs defragmentation are not exactly right; using Repair Permissions in Disk Utility will not "defrag" the hard disk, but it will accomplish the same purpose. Actually a Mac should be checked for fragmented files every year or so, but this is best accomplished by a professional with special software designed for use in a multi-step analysis.

So what does this have to do with an SD card. Well, an SD card is formatted in the camera with a universal protocol readable by Win and Mac. There is really no easy way to defrag a static memory base, save reformatting in the camera. And for those of you who have been using the same SD card in all your cameras for 10-15 years without ever formatting the card, Good Luck!

Finally (and I will admit this is hearsay, albeit from a reliable source), SSD's apparently do not need any type of realignment or defragmentation. If this has been proven untrue, I would appreciate someone informing me. Thank you.

Jimmy T Loc: Virginia

WF2B, I concur with you. I also routinely chimp and delete sub-par pics on my 6D, 7D and p&s cameras, and I have never had any issues. I'm not arguing, just saying. Just another data point to consider.

BHC Loc: Strawberry Valley, JF, USA

If you are using a 64gb card and delete pictures when the card has 32-48gb of pictures on it, I doubt you'll have problems. Most people have problems with deleted/overwritten images when they have 7.5gb on an 8gb card and start deleting. Note that the numbers used above are examples only. Similar problems can happen to anyone who pushes an SD card to its limit.

JimH123 Loc: Morgan Hill, CA

This is true. There is no speed advantage in defragging a SSD drive, or just a SD card for that matter. There is no head to move. The time to access any sector is the same. Whether the sectors are stored sequentially, or not, just does not matter.

What defragging on a SSD or SD card does is to wear it out faster. Defragging does massive reads and writes as it moves things around to make the sectors sequential.

BHC Loc: Strawberry Valley, JF, USA

Thanks for the response and information. One question: When there is insufficient space to store a file in adjacent sectors, does SSD automatically rearrange files or does it store files in a fragmented manner?

Apaflo Loc: Anchorage, Alaska

It stores them in a fragmented sequence. That has no effect on normal use.

The numbered sequence is physically random already! It just doesn't make any difference

The only effect, which you will likely never experience, is that one type of very simple file recovery will not work. File recovery will have to be done with one of the more complex sophisticated programs. The chances are good that no recovery program you will ever own will be affected by fragmentation.

frangeo Loc: Texas

I heard that some photographers had this problem. Not sure of the camera they were using. I've deleted in camera 10's of thousands of times on CF cards with no problem. Some of my CF cards are so old that the paint is warn off and I don't even know what brand they are. However, if your worried then just don't delete.

JimH123 Loc: Morgan Hill, CA

I suppose that erasing images in camera could cause a potential corruption problem. But remember that erase is not really erase. It is only a tweak to the File Allocation Table which tells the cameras operating system that the space held by that image is now available for use. But when the camera goes to reuse that space, some things have to happen.

Flash memory can only be written to if it is already erased. And the way flash memory works is that the memory is divided into blocks. People normally call them sectors, but in flash memory nomenclature, a sector is a unit in which Error Correction can find and fix bit errors and there are typically 16 sectors per page. This is something that is invisible to the end user. But back to the blocks. A block consists of some number of pages. Common numbers may be 256 pages, or 512 pages. Current MLC (Multi-Level Cell) devices may have around 16K columns (each column holds 8-bits or 1 byte). Supposing we have a device with 256 pages, and 16K columns (I am leaving out the extra columns used by ECC to do the error correction since you are only able to access the 16K), then we have a block size of 256 x 16K = 4MBytes. So let's suppose we have a 24MByte file that we are saving (and let's suppose it is exactly 24MBytes for this discussion). Then it consumes exactly 6 blocks. If you erase an image in the camera, these 6 blocks are marked as available and when the camera needs to reuse them, it has to erase just those 6 blocks and to then store the new image into that same place.

But numbers never really work out so nice, so it is very likely that the image may be slightly larger than 24MBytes and it now needs 7 blocks. Now here is where I am not 100% sure what the camera operating system does. But I think that the unused portion of that 7th block remains unused and no additional image will attempt to make use of this space. Thus this is wasted card space. And this is the reason that the camera reports "about" the number of images that can still be recorded to the card. The next image of the same size will use its 6 full blocks and spill over into a 7th block, but all that additional 7th block space also goes unused.

To reuse space, the cameras operating system must correctly erase each block that is intended to be reused and to not make any mistakes in doing so. If there is any quirk to the camera operating system, I suppose something bad could happen.

I was also going to suggest that the camera may operate slower since it has to erase all the reused blocks. But on second thought, I am not going to suggest that since a normal format also does not erase the individual blocks. The data is still there and can be retrieved. Thus no matter whether you erase individual images or just let everything happen without deleting, I think there will be no speed penalty.

BHC Loc: Strawberry Valley, JF, USA

Thanks for the explanation. One more question... can the storage of files in fragmented sequence on a SSD result in slower retrieval as it can on an HDD?

JimH123 Loc: Morgan Hill, CA

No, fragmented files on an SSD, or any flash memory for that matter, do not equate to slower read access.

JimH123 Loc: Morgan Hill, CA

It does not rearrange them. Once they are written, they stay where they have been put. Fragmentation is not an issue that is important to this kind of memory.

JimH123 Loc: Morgan Hill, CA

The only problem with old cards is that there is limit to the number of write/erase cycles that a card will accommodate. These memory cells will eventually wear out. The older technology, SLC (Single Level Cell) were more robust and could survive 10's of thousands of write/erase cycles. The newer MLC (Multi-Level Cells) have much larger memory space, but at the cost that they will wear out faster. SSD drives take this into account and do something called wear leveling in that it keeps track of how many times a block has been erased and as it hits some limit, that block is marked as not to be used any more and a new block is selected for that data. This can result in tremendous fragmentation, but fragmentation is not a problem for this kind of memory.

The SD cards (or CF or any other kind of flash card) do not have wear leveling. You can keep using the card up to the day it fails. If a card stops working, perhaps it can be recovered in a low level format, but not all formats are up to this task of marking bad blocks. I have found that by the card reaches this point, there isn't much sense in trying to keep it going for a little while longer since if one block and worn out, other blocks are shortly meet the same fate. When I find a card that is messing up, I get rid of it.

JimH123 Loc: Morgan Hill, CA

To reuse space, the cameras operating system (which the camera manufacturer is responsible for) must correctly erase each block that is intended to be reused and to not make any mistakes in doing so. If there is any quirk to the camera operating system, I suppose something bad could happen. By quirk, I mean that perhaps the camera operating system is not quite as robust as some PC's operating system and perhaps may make some mistakes if images have been deleted and its doing things out of order. This is just a guess. Some report deleting thousands without any issues, and others do report seeing issues. Could this be a problem with certain camera manufacturers? Or certain models? And if a model had a problem, is it fixed in a newer model? I personally have never had an issue and have deleted many an image. Perhaps a tally of what makes and models have seen a problem would be interesting?

TriX Loc: Raleigh, NC

Good information. Especially interesting that you mentioned the wasted space if a write does not exactly align with the number of blocks. You're correct - the extra unused space on that 7th block would be wasted. In fact, it's this phenomena that can account for substantial wasted storage space. If the user/application has control of the write size, then of course you try to have the write exactly the size of of a given number of blocks. Since this isn't usually possible for a non-commercial user, your recourse, if your file system provides the option, is to pick an appropriate block size for the files you're storing. On a HD storing large (image) files, larger blocks, requiring less head seeks, provide faster performance, but waste more space if the write isn't aligned. Imagine a 24.2KB write and 2KB blocks - you waste 1.8KB of the of the 13th block or ~ 8% of the storage. On the other hand, if you choose 512B blocks, you only waste 300B - just over 1%, but you use 4 times as many head seeks and take a performance hit. Note that the wasted space applies to both flash and spinning disk, while the head seek penalty applies only to HDs.