CF card as HDD?

[spotdog14]

Ok, I am debating getting a 16 gig HDD and using it as my system disk? What are the pros and cons of this?

What type of speed do these things support, would it be faster than a 7200 rpm drive?

 

[axan]

CF cards are painfully slow, we are talking like 30mb/s read and 25mb/s write for the extreme performance versions( $$$) you would be better off getting a SSD like mtron or one of those new ocz ones

 

[mindedc]

Slow and dangerous. If you have things that write to the disk a lot, you can prematurely wear out the disk. Of course you can fix these things by turning off virtual memory etc, but as the above poster indicated it's not a great idea.

The one place it is good is for thin embeded systems and umpcs like the eeepc from asus. I use cf cards to boot off of for linux servers with software RAID. That lets me always have a /boot with minimal risk of not being available at boot time, I can then raid the root with whatever filesystem I like and don't have to worry about boot loaders.

 

[Joe Average]

CompactFlash doesn't have the technology built into newer forms of Flash-RAM based products known as wear-leveling which keeps an eye (so to speak) on the usage of each and every cell of data storage. When data is written to a cell, a notation of sorts is made in the monitoring circuit of the date/time (more or less) and in the future that information is used to determine whether a write pass will actually write to that specific cell again or another.

The theory is that if you could have a device of a given size and only write one single pass of data to each memory cell one time, the device would fill up before you ever wrote another byte of data to the exact same cell a second time. Even if you deleted the data located in cell 1, the next piece of data to be written would not automagically go into data cell 1 because it's been written to in the overall first pass - it won't get hit again till the second overall pass begins, if that makes sense.

Reading from Flash-RAM can happen nearly infinitely, it's writing data to a cell that damages it and each cell has a limited number of write cycles, obviously. CompactFlash never had that type of wear-leveling by design so, as the other posters have said, using a CF card of any kind or size is just asking for trouble with such intensive read/write operations that a typical hard drive deals with in even a single day of severe usage.

 

[msabo]

^^ spot on. Also, as for 16GB, I don’t know what O/S you are thinking about, but I just did a build with Vista 64x OEM and it was 25GB.

 

[unhappy_mage]

CompactFlash doesn't have the technology built into newer forms of Flash-RAM based products known as wear-leveling which keeps an eye (so to speak) on the usage of each and every cell of data storage.

Not necessarily. Wear leveling isn't form factor-based; CF cards can have it too. The Ritek cards I have use dynamic wear leveling, meaning they will not move unchanging data to new sectors to even things out more; instead, only blocks that go bad are (transparently) re-mapped and replaced.

 

[bexamous]

I run off 3 CF cards, one CF for /boot and /tmp I think and the other two in raid0 for rootfs. /home is then on a hd array. Writes are noticeably slower than a hd (ie when doing updates) but when opening a new program or doing a find on root or something it feels sorta fast. I really only did it for fun and wouldn't recommend it as a good idea. No problem with the cards failing or anything, 266x adata cards, I do do backups hwoever .

 

[bloodlet]

I've seen people setup FreeNAS with a CF card as their boot HDD which is a great idea. Otherwise, too slow.

 

[hjreggel]

Not necessarily. Wear leveling isn't form factor-based; CF cards can have it too. The Ritek cards I have use dynamic wear leveling, meaning they will not move unchanging data to new sectors to even things out more; instead, only blocks that go bad are (transparently) re-mapped and replaced.

That's absolutely correct. Normal flash cards assume to be filled up to the rim and then re-formatted. A modern SSD controller is supposed to keep a record for each cell, and swap static data from fresh cells on heavily used cells and try to keep all cells at about the same "age".

If you want to see what current CF cards can do, see
UDMA CF Cards

If you still want to use CF cards as SSD, you should know the basics about flash cards regarding cell size and alignment, and make sure that the clusters of the filesystem are at least the size of an erase unit, and properly line up with these.

 

[mindedc]

IF you insist on doing this on linux you can set the mount option "noatime" and it will reduce the excessive writes by not updating the access time on files... I would try and keep the "highly variable" disk areas like /var on spinning disk and I would run a ram disk for temp......

I have also found its difficult to get DMA working correctly on the CF cards. For my purposes its a moot point so I have invested little time on it....