Go Back   Steve's Digicams Forums > Digicam Help > Memory Cards, Microdrives, Card Readers

Reply
 
Thread Tools Search this Thread
Old Oct 17, 2003, 2:07 PM   #11
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,544
Default

Quote:
This IS an issue with hard drives becuase there is actually a mechanical component that has to move further or more often with fragemented files than if all files were stored contiguously. Memory cards have no moving parts at all. Is fragmentation really an issue with memory cards? I now think it is not. Files should not be corrupted even if their blocks are thrown all over the place.
... Really?

NAND Flashes, (the kind used in flash cards) are organized in even smaller blocks than sectors are in disk, then go through a physical to logical format conversion either in software like in SM or hardware in a controller in CF.

DOS fat is fat, ie it's the same File Allocation Table in any format and the same addressing issue still apply! Will FORMAT make defrag redundant?
NHL is offline   Reply With Quote
Old Oct 17, 2003, 3:00 PM   #12
Senior Member
 
Join Date: Aug 2002
Posts: 2,162
Default

........Files should not be corrupted even if their blocks are thrown all over the place...........

Yes, but then users complain their read/write times are increasing because instead of reading a contiguous file, the actual bytes read increases because of all the pointer addresses, not to mention the wasted space because lots of small spaces means lots of slack spaces.

Use WinHex sometime to scroll through a card full of fragmented files. The other downside is you stand a better chance of image recovery if you accidentally 'erase' or 'soft format' a card if there is only one FAT pointer to the start of a contiguous file block. Fragment a card and there is more chance even a small file fragment will get over written and your file is corrupt and only partially recoverable. An image with a large black lump where the missing image should be, is not something Photoshop is good at! VOX
voxmagna is offline   Reply With Quote
Old Oct 17, 2003, 4:03 PM   #13
Senior Member
 
Join Date: Mar 2003
Posts: 438
Default

The point is that there is a latency associated with disk access and also with the time needed to physically move the arm containing the heads. This does not exist in flash memory.

In the FAT system there is a pointer to each and every block in a file even if the blocks are located contiguously. It's the physical aspect of a hard disk that makes speed suffer with fragmentation. The number of accesses does not change regardless of the way a file is laid on the media - you still have to read the same number of sectors.

I agree that fragmentation may make recovery harder, but I don't really think it will affect read/write speed at all in flash memory media.

If someone can provide some link to a source proving me wrong, please post it here. I could be wrong.

Anyhow, the solution has been mentioned here before. Don't delete pictures in the camera and when transferring to the hard disk either delete the whole thing at once or reformat the card.
luisr is offline   Reply With Quote
Old Oct 17, 2003, 4:34 PM   #14
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,544
Default

I guess those 2M/4M/8M data buffers that the manufacturer installed in their hardisks are for not then... Or could it be that they've use the same idea to improve the write time in flash?
NHL is offline   Reply With Quote
Old Oct 17, 2003, 4:36 PM   #15
Senior Member
 
Join Date: Dec 2002
Posts: 5,803
Default

NHL

"FORMAT" will certainly make defrag redundant, when format can be used. By definition when you copy files back to the newly formatted disk the computer writes the files one at a time. It will write them contiguously and no defrag will be necessary. The trick is that you can't do it often with most devices (hard disks in computers) but you can in cameras/mp3 players and such. So for cameras, defrag really isn't necessary. Itís a usage thing. For computers, where you (basically) never take everything off the drive, formatting (instead of defragging) is not really an option.

[quote="voxmagna"........Files should not be corrupted even if their blocks are thrown all over the place........... [/quote]Exactly correct. This happens all the time on computer hard disks. If there is corruption it isn't because the file is broken up into fragments and put all over. Itís because of a bug in software (or a defect in the hardware.)


[quote="luisr"}I agree that fragmentation may make recovery harder, but I don't really think it will affect read/write speed at all in flash memory media.

If someone can provide some link to a source proving me wrong, please post it here. I could be wrong. [/quote]It very well could have an effect on write and read speed. Having written drives for flash memory chips before (not imbedded into CF, but in a different type of product) I have some experience with this.

Here are some reasons why:
I assume there is some cache memory in the flash chips. That it is more efficient to read contiguous flash segment (flash chips are broken up into chunks, or segments. Each segment must be written to completely.) Flash chips donít have to have this, but I believe some do. It would certainly improve performance.

If multiple segments are on the same chip, I believe that some modern flash memory can be put into a write mode and you can specify which segments will be written to, and it will prepare them for writing more efficiently than if they were on separate flash chips.

So to me it is very easy to believe of a way that writing would be slower to a CF which is fragmented.

Itís slightly harder, but still imaginable that reading would be faster.

There is also the anecdotal evidence that people have posted statements like ďmy CF card has gotten slower since when I got it. Instead of writing the picture in 5 seconds, it takes 15.Ē We tell them to reformat the card in the camera and they say itís back to the fast times it had originally.

Eric
eric s is offline   Reply With Quote
Old Oct 17, 2003, 5:22 PM   #16
Senior Member
 
Join Date: Mar 2003
Posts: 438
Default

I have to ask this. Is it customary for people to use their memory cards for long term storage?

I normally take my pictures and once I am home I download the whole thing to my hard disk and delete all files from the memory card. It seems that many people don't work with their media and digital pictures this way. Also, I usually don't delete "bad" pictures right away. Pictures that look "bad" in the tiny LCD screen at times look good enough to keep when seen in the computer screen. Sometimes they can be rescued with some post-processing.
luisr is offline   Reply With Quote
Old Oct 17, 2003, 9:37 PM   #17
Senior Member
 
Join Date: Dec 2002
Posts: 5,803
Default

I spent the money so I wouldn't have to care (much.) So I got a 1G and 512MB cards. Not many can afford to do it, I realize.

With that understanding, I don't delete. I do review (especially if it was something really cool) but I donít delete. I always copy the entire set of pictures and then I (almost immediately) put the card back into my camera and reformat. I do this for three reasons:
1) So I donít forget the card in the reader and go out without it. Iíve only done this once.
2) So I always have the max capacity in the card. On a really good day, I can take 350+ pictures in 3 hours.
3) So I donít risk doing something to the card in the computer. Not likely, but why risk it?

I do agree about rescuing. Some time I need to adjust the brightness of the LCD so it looks reasonably close to my monitor. Iíve seen things which look really dark on the camera turn out to be savable in PhotoShop.

Eric
eric s is offline   Reply With Quote
Old Oct 17, 2003, 10:11 PM   #18
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,544
Default

On the surface things looks simple, but in practice a flash device is quite complex, and Eric seems to have the closest idea of what's involved 'really' in accessing a NAND flash devices, ie the type use in flash cards for bulk serial data (vs the NOR type of flash which can be random accessed and used on PC motherboard for code storage):
http://www.samsung.com/Products/Semi...o/app_nand.pdf

1. Flash devices are organized by blocks and pages. A page access is faster than a block access. One can also not erase or write a piece of data at time. A whole block has to be erased or written even though only one piece of data need to be changed (ask Eric)!!!

2. To do a write the controlling device, @ the low-level, has to issue a command sequence, write the data, and then continously poll a status until the data is ready, and then terminate the sequence by issuing another command (page 12 of the above link). Provided there are no error otherwise the block is mapped out!

3. Unlike a hardisk which is designed for native FAT, flash devices need a translation layer (see page 3 of the above link) to convert the sector address to physical addresses of the flash...

4. Also don't forget to checkout the Error Correction on page 6 or Invalid Block management on page 8.

In summary, instead of debating the merit of flashes vs hardisks. This is what everyone should do:
o Copy all images to the PC.
o Format the memory card in the camera before re-use.
o Deleting a few pictures to free up space is OK.

-> Repeated deletions without a format is not a good practice!
NHL is offline   Reply With Quote
Old Oct 17, 2003, 10:17 PM   #19
Senior Member
 
Alan T's Avatar
 
Join Date: Jun 2003
Location: Chester, UK
Posts: 2,980
Default Re: Deleting vs. Formatting

Quote:
Originally Posted by calr
Can someone please elaborate on this and advise me the best practice to follow in handling deleted images.
Here's a different view from most replies in this thread....

Both of my digicams have had a simple quick 'delete' button to allow me to tidy up when I'm sure I've just acquired some garbage - completely wrong exposure; chopped someone's head off; didn't get there in time for the delayed action shutter; one shot of 5 bracketed exposures clearly better than the other 4; hopelessly misfocused due to wrong focus mode; camera set to ISO800 when I wanted ISO50; etc., etc. This is one of the great advantages of digicams over film.

When it comes to storing everything permanently on your computer later on, it's a great help to have things in reasonably good order already. If you're like me when I return from holiday, you may not be able to remember what happened when.

Also, when you're on holiday/vacation, space on your cards may be useful, unless you're wealthy and have lots of big cards, and lots of well-charged batteries, and a porter to carry all the gear. You're supposed to be enjoying your holiday, and even looking at the scenery as well as photographing it.

All the technical issues are well covered elsewhere in this thread. I suggest you tidy up as you go along, if you feel so inclined. Use a hand lens on the LCD screen in a dark place to get a better review if you need to. Then, back home, transfer the lot to your computer, write-protect these original files, and back them up (e.g., on CD-R).

THEN do your final tidying, twiddling. etc, on copies of the files, and reformat the camera's memory card, in the camera.
Alan T is offline   Reply With Quote
Old Oct 17, 2003, 10:22 PM   #20
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,544
Default

Quote:
... and reformat the camera's memory card, in the camera.
That's sum it all!

Amen :P
NHL is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 6:19 PM.