using compact flash for data logging

Hi,

I'm developping an (among other things) data logging application. I've been planning to use compact flash as storage medium, to eliminate heat and moving parts of hard drive ( the system will live in environments with vibration ).

I am aware of problems with limited write cycles in CF, but I think a sandisk industrial CF should last me several years. However, I recently read that powering off the machine will the CF is writing can kill the card. Is this true for all controllers ?

I'm using an advantech 5820.

thanks Ricardo

Reply to
Ricardo Trindade
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Nobody guarantees how a CF works in non-standard situations like long lasting heavy write access or power down while writing :-(

-Michael

Reply to
Michael Schnell

Hello Ricardo,

Nothing is 100 % save. If you use a normal harddisk, it also can become defective, as well as any other part of the system.

You have to define which risk you can accept.

The risk, of course, mainly depends on how often you write to the CF. Obviously it is a difference if you write every few seconds or only every one hour.

Regarding power loss: I am not sure, but I think I have seen a posting once that sandisk will not become defective at all but some sectors can get errors. He wrote, that after reformating everything works fine again. So maybe a journalling filesystem would help. There were already many discussions here, I did not get a clear view about it. Maybe you should look at the old discussions (try google).

About the risk: I write every 10 minutes to the disk and this takes less than 1 second (you see, I have not so much data). So the change would be 1/600 that a power loss occurs during writing. And I do not believe that the card becomes defective at every power loss when writing (Question: could anybody estimate this risk?). So in worst case every 600 years data would be lost if there is ony power loss per year. For my application this is sufficient.

BTW: I did not have a data loss in 100 (devices * years) up to now.

Greetings Ernst

Reply to
Ernst Murnleitner

I don't think it'll destroy the cf card. I'd say it depends on how often you write to the card. If you're heavily writing to it, then I'd watch out. I'm doing my development on an advantech board, but not one as beefy as yours. Is your final product going to be battery powered or plugged into an outlet? If you're running on a battery, there are many solutions out there for battery monitoring chips that have linux drivers in them. If they're going to be built into the board, that'll be a handy utility. Most of the products we make have a wall option, but should that kick out a battery immediately kicks in and prevents any power going out...that is, of course, until the battery dies.

I don't know of any cf cards going nuts if they get killed in the middle of a write. If it's something that happens once in a lifetime, there are data recovery tools where you can pull the information off in raw bits and reconstruct the file structure on another system to recover your data.

Depending on your environment with vibrations, if you have a rather steady temperature range (sadly, like 3 degrees C to 37 degrees C) and you're not sure about the CF card, you may also want to look into laptop hard drives. A lot of the ibm and the drives they put in panasonic toughbooks (i don't remember who makes those) come with gravitational sensors that provide a serious amount of read/write head protection. In fact, I think a lot of the new laptop drives do that. The schematic of your board

formatting link
has an eidi interface...you could always just get a converter to hook up a laptop drive.

Those are just ramblings, but suggestions non-the-less. There are always alternatives if you don't trust your cf card.

Reply to
ant

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