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Author Topic: CF card as hard drive?  (Read 8369 times)

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Offline Floid

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Re: CF card as hard drive?
« on: February 13, 2005, 02:58:03 AM »
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Generale wrote:

Especially if the person is willing to put a small slot in their case so they can exchange drives  :-)


Remember that, depending on the design of the adapter, hotplug should be considered dangerous.
 
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Only thing is, I have no idea if they require drivers, because the connection appears to be pretty much straight-through.


The types of adapters likely to allow hotplug are likely to require some sort of driver support.  (Note that I'm talking about ones that hang off the IDE bus; USB and so forth are generally fine, or at least marginally more insulated from frying the system.)  The 'pretty much straight-through' kind will be fine, but you may wish to refrain from hotplugging those.

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Any thoughts?


If write cycles are a concern, see if you can scrounge a Microdrive instead of a truly solid-state card.  Access speeds may be even worse, though.
 

Offline Floid

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Re: CF card as hard drive?
« Reply #1 on: February 13, 2005, 01:00:39 PM »
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MaDDuck wrote:
Given the fragile, unbuffered nature of the in-built IDE's on 600/1200, it might be a good idea not to even concider a hot swap option at all!


Well, AFAIK, this goes equally for all controllers not specifically built for CF (which are then probably driving the card in 'native CF mode,' however that works).  There are, however, weird IDE<->CF bridges with some smarts to them, that take care of the buffering and so on, but I have no idea how standard they are, what device class they intend to be, etc... only that they aren't likely to allow mounting at all until someone specifically crafts support, considering even Linux and the BSDs have or at least have-had trouble with them.

I mentioned this 'risk' a long time ago, and I think someone may've called me on it or otherwise elaborated, but basically, if it looks pretty 'straight through,' it's likely to work, and if it has a big ASIC present and comes bundled with a Windows driver CD, caveat emptor.
 

Offline Floid

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Re: CF card as hard drive?
« Reply #2 on: February 14, 2005, 11:37:12 AM »
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Generale wrote:

As for microdrives. If I got hold of one of them it'd go straight into a Fujitsu Stylistic 500 I have. Odd machines, but strangely cool.


That takes CF?  I gather the old style of PCMCIA (Type III?) hard drive was used on those designs... though I suppose a flatter solution might buy you a slot, depending how they have it arranged.  (If you really like those, they took them way past the 486 era, and may have only just renamed the brand as part of the TabletPC mess, I've lost track.)

---

As to the remapping, I'd assume that's snuck in, too (especially as the broader market is forced to use FAT on all these), but even in the best case, how many spares are you guaranteed?  The MTBF is probably more than fine for an Amiga -- it certainly works for palmtop users -- but you probably wouldn't want to put something like a swapfile on one.

Edit:  Okay, specifically, I'm digging at "dynamically map bad blocks/exhausted blocks out of the available space, and use another sector," just to make sure everyone knows what this means.  Drives aren't filesystem-aware, and most filesystems aren't drive-aware to this extent (whether they should be is another question), so the on-disk logic can remap blocks, but can't shrink the 'available space' of the volume -- at least without, pardon the pun, fscking up the assumptions made when partition tables were written and filesystems formatted.  After that limited number of spares behind the curtain are used up, it's time for the card or drive to hit the bin.  

It would be kind of cool if they'd just shrink the capacity of the drive on you when you run out of spares and let you reformat (perhaps reserving another row's worth of spares each time, until the capacity of the card's down to 0), but there's also kind of no way they can do that without risking access to all your data at the moment, so a) I'm almost completely certain they don't do that, and b) they won't be able to unless 'a miracle occurs' at the host level.  It's a lot easier to make the host do it in software -- no coherency concerns, no need for the host to take this 'whoops, we just changed the size of the volume on you' exception at *any* time -- so I gather 'soft' mechanisms and more flexible filesystems are becoming the popular approach for dealing with unreliable media.  The other alternative would be to have all sorts of 'mailbox' logic until your humble USB stick becomes its own fileserver, but that's a lot of firmware for what's supposed to be a 'disposable' storage device... still, there are compromises to be made, if I understand how CD and DVD packet-writing actually works at that low level.  ('Mailboxing' files gets ridiculous, but 'mailboxing' blocks/sectors/packets just acknowledges what the disks are doing already, and there's a good excuse to let them carry on, what with latency and buffer-lifetime issues if each remap has to be handled 1980s-style by the host.)

My bet is that even, say, Mt. Rainier isn't quite as smart as I wish it is, but after doing all this thinking in public, I'm going to have to look into it now.
 

Offline Floid

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Re: CF card as hard drive?
« Reply #3 on: February 20, 2005, 08:04:28 AM »
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Generale wrote:
Too tired to format this properly. Sorry. But,

The stylistic has 2 pcmcia for normal use and 1 doublewidth for microdrives if I remember correctly.


To spare you the pain of buying the wrong thing, CF and PCMCIA/Cardbus are different.  Modern microdrives are only available in CF form-factor (and I seem to recall there's some 'typing' of CF slots as to whether they're thick enough to let the microdrive fit), but PCMCIA hard drives exist -- they're basically a 1.8"? drive crammed on a hardcard, hence the sheer height of that Type II or Type III PCMCIA slot.

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Now for the bad blocks.
Are you saying that microdrives are smart enough to implement the same sort of system as S.M.A.R.T. Ie, having some capacity put aside for bad sectors that is dynamically remapped, and after that threshold has been hit, 'Sorry but you have bad sectors'. Anyway, I don't see how it could be too much of a problem, because as long as the CF card has the ability to say 'this byte is bad', the filesystem handles the bad blocks anyway.


Someone's saying this... the microdrives really ought to, being magnetic and prone to a certain defect rate, and you can probably find out if they do or don't in the product literature; the question is whether they bother doing this for (any? all? some?) of the fully solid-state cards in any of the various formats they come in (CF, SD, USB stick)...

Bad-block remapping is sort of independent of S.M.A.R.T., which, as far as I know, is not much more than a buzzword out in IDE land.  They were, in theory, doing remapping long before anyone came up with the S.M.A.R.T. word and the limited ability to let the drive report an 'I personally think I'm about to die for reasons that may or may not be accurate' condition.  (Per this article, I notice IDE S.M.A.R.T. has wobbled a bit in nature, which explains my confusion.  Since I'm more of a SCSI guy, I've been able to count on spare-table statistics showing up in mode pages, whether or not its presence there is some requirement of a 'S.M.A.R.T.' spec.)

Also, while Amiga and MS-land filesystems can still deal with bad sectors exposed to them at the software level, not every platform is so lucky.  In particular, the code to handle that appears to have suffered 'some' abandonment in BSD-land, and not every *NIX filesystem will bother with the automatic reallocation that makes life on a dying disk comfortable.  (This may have something to do with cultural differences, or maybe I just haven't found the best-practice for creating a soft list in BSD-land.  A major problem is, of course, what happens when the sectors containing the bad blocks list go bad, or when a cabling or UDMA mode problem suddenly makes 'every' block on the disk look bad...)

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I just had a stupid idea that I shot down instantly. Just thought I'd say it because some people might get a laugh out of it. My logic went as follows:

*CF would wear out too quickly if used for swap.
*What doesn't have the writing limitations?
*RAM doesn't!
*So use a Ramdisk for virtual memory!!
*.....idiot.


The other day I caught myself thinking about creating a VM-backed /tmp, then moving the swapfile to it, because it doesn't have to persist across a reboot, and it would only have to swap when the file grew...  :-D