Messages in this thread |  | | Date | Mon, 10 Mar 2008 09:22:13 +0000 | From | Alan Cox <> | Subject | Re: [ANNOUNCE] Ramback: faster than a speeding bullet |
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> So now you can ask some hard questions: what if the power goes out > completely or the host crashes or something else goes wrong while > critical data is still in the ramdisk? Easy: use reliable components.
Nice fiction - stuff crashes eventually - not that this isn't useful. For a long time simply loading a 2-3GB Ramdisk off hard disk has been a good way to build things like compile engines where loss of state is not bad.
> If UPS power runs out while ramback still holds unflushed dirty data > then things get ugly. Hopefully a fsck -f will be able to pull > something useful out of the mess. (This is where you might want to be > running Ext3.) The name of the game is to install sufficient UPS power > to get your dirty ramdisk data onto stable storage this time, every > time.
Ext3 is only going to help you if the ramdisk writeback respects barriers and ordering rules ?
> * Previously saved data must be reloaded into the ramdisk on startup.
/bin/cp from initrd
> * Cannot transfer directly between ramdisk and backing store, so must > first transfer into memory then relaunch to destination.
Why not - providing you clear the dirty bit before the write and you check it again after ? And on the disk size as you are going to have to suck all the content back in presumably a log structure is not a big concern ?
> * Per chunk locking is not feasible for a terabyte scale ramdisk.
And we care 8) ?
> * Handle chunk size other than PAGE_SIZE.
If you are prepared to go bigger than the fs chunk size so lose the ordering guarantees your chunk size really ought to be *big* IMHO
Alan
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