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Linux file system advice needed please - Page 3

post #21 of 51
Thread Starter 
Quote:
Originally Posted by lloyd mcclendon View Post

have you considered using different mount points

/ ext4 ro
/a-lot-of-stuff ext4 ro
/the-writeable-stuff some-other-fs rw
/some-more-writeable-stuff that-other-fs rw

you should be able to organize the dirs to keep the rw stuff in one mount point. lvm could be of assistance here. I've seen kiosk systems built this way ... and the RW parts are throwaway each boot.
That was what I said I was going to do in the opening post. However I still need a file system for the tiny none volatile rw mount point. (Everything else is either ro or ram disk so a none issue)
Edited by Plan9 - 2/6/13 at 6:03pm
post #22 of 51
What about NILFS? It's logs instead of a journal but it sounds kind of like a RAID0 to me in that any power lose or crash simply restores a prior image without a fscheck if I understand it correctly...redface.gif

http://www.nilfs.org/en/about_nilfs.html
     
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post #23 of 51
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I did look at that but thought it might be a little overkill. looking again, I think I might do some testing with it now though.
post #24 of 51
Thread Starter 
It is going to be overkill because I'd need quite a large partition just to use nilfs (it wouldn't let me create a 5MB partition). frown.gif
post #25 of 51
Quote:
Originally Posted by Plan9 View Post

It is going to be overkill because I'd need quite a large partition just to use nilfs (it wouldn't let me create a 5MB partition). frown.gif

LOL. Oh yeah, I think it's designed with more space in mind. But what do you plan to do with such small partitions anyway? I can't think of an OS let alone any programs outside of some terminal ones that are that small. Well, I'm still curious what you'll choose anyway.
     
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post #26 of 51
Quote:
Originally Posted by Sarec View Post

AFAIK phones don't give direct access to the SD-card. They lie to the system kinda of like an API or fake HDD. Might not be true for the 'additional' cards you can add to a phone. I could be off base though. This is mostly hearsay from what I have read and heard.

Oh and dear me.. Double posting with enthusiasm.

Flash devices come in two forms (generally). Either they directly expose the flash medium, and require that the filesystem you use deal with maintaining the flash (things like YAFFS are designed in this fashion), or they have an extra internal layer that exposes a simpler device that behaves more like a spinner (SSDs, SD cards, and many phones internal memory do this). Generally speaking, if you device has that extra layer (and it is a half decent implementation), then you should use it with a regular FS.
post #27 of 51
Quote:
Originally Posted by Plan9 View Post

ah sorry I thought I'd said

Anyhow, journaling will add a whole load of additional issues in the case of power failure due to the journals. And if the journals get trashed then the entire file system will fail. What I really want is the file system to be intact even at the risk of the files occasionally getting corrupt.
That will force file system checks though - which is exactly what I'm trying to avoid

I don't understand why you are trying to avoid a journaling file system. The whole point of one is to make the filesystem remains consistent. If you go with something like ext2, then on any unclean shutdown you have to preform an expansive check on partition, potentially having serious data corruption. With ext3/4, that check is significantly smaller, as the journal is replayed and everything continues as normal.
post #28 of 51
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Quote:
Originally Posted by Rookie1337 View Post

LOL. Oh yeah, I think it's designed with more space in mind. But what do you plan to do with such small partitions anyway? I can't think of an OS let alone any programs outside of some terminal ones that are that small. Well, I'm still curious what you'll choose anyway.
You're right, I've not really explained what I'm doing:

I'm building an in-car MP3/FLAC audio system. There's only going to be a couple of text files:
a list of the entire contents of a USB HDD (so when it's powered on, it knows exactly what's there and can start seeking the 1st track in 1 thread while a 2nd thread re-catalogues all the files to see if the contents have changed).
and the file name of the current song being played. So if the power is cut (eg you turn the engine off), then you start the car up it knows where to start playing from again

The 1st file is only going to be written to once at the start of journey and the 2nd is only going to be written to when the next track plays. So the chances of a power cut while the file is being written to is very low. However if that does happen, then the software will spot a corrupt file and just revert it to factory settings (ie start playing from the 1st track on the USB HDD)

So I'm really not worried about file corruption. It's only the file system that needs to survive.
Quote:
Originally Posted by MJD View Post

I don't understand why you are trying to avoid a journaling file system. The whole point of one is to make the filesystem remains consistent. If you go with something like ext2, then on any unclean shutdown you have to preform an expansive check on partition, potentially having serious data corruption. With ext3/4, that check is significantly smaller, as the journal is replayed and everything continues as normal.

But that's the whole point - I'm not bothered the file integrity, I don't want extra crap in the fs which requires additional checked for consistency and I don't want delayed start up times due file system checks.

Literally all I want is an empty container that I can dump 2 or 3 files into it. If those files corrupt due to a write during power failure (which is only a slim chance anyway), then I'm quite happy for those files to get trashed.

Journalling adds a whole level of complexity which will only result in the fs itself getting trashed.
post #29 of 51
i think you'll find that all of these types of devices have the luxury of a secondary power source

e.g. your car radio is hooked up to the 12V and 5V, when you cut the engine it kicks over to the 5V to do housekeeping ... save where it was, and keeps drawing from it to store your presets etc. Then you disconnect the battery and all is lost.

so, have you at all considered one of those small micro usb battery pack things for the pi, one that would basically serve as a UPS .. and you'd trap when the main power was cut and perform your hibernate .. never shutdown wink.gif

I think it's theoretically impossible to always guarantee what you need with only a primary power source that can go at anytime. Hopefully someone else has some better thoughts, as I am interested in a similar type project with my PI as a GPS in the car
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post #30 of 51
I know this isn't the type of answer you are looking for but it might be a possible solution. I assume you are going to power your raspberry pi through something similar to USB Car Cigarette Adapter, I have something similar that charges my cellphone in the car. My cell will charge even when the car is off. Assuming your car continues to send power to the cigarette lighter like mine does, the only times that I can think of when the power to the PI could be lost is when you car batter dies (of course) and possibly when start your car the starter might pull enough amps that power to the PI gets interrupted. To prevent one of those events from interrupting your PI you could purchase something similar to USB Battery Pack.

Essentially you'd plug your PI into that battery pack and then that battery pack into your car. The car keeps the battery pack charged and the battery pack should supply power for your PI for up to nearly 3 hours ( there are larger battery packs if you think that 3 hours isn't long enough. This battery pack is able to supply up to 700mA and from the Raspberry Pi site that should be all you need.
Quote:
Model B owners using networking and high-current USB peripherals will require a supply which can source 700mA (many phone chargers meet this requirement). Model A owners with powered USB devices will be able to get away with a much lower current capacity (300mA feels like a reasonable safety margin).


Hope this helps
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