Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressed by regarding reiser4 inclusion]

From: Kyle Moffett
Date: Tue Aug 01 2006 - 22:26:53 EST

On Aug 01, 2006, at 19:50:49, Ian Stirling wrote:
You probably don't actually want to flush the cache - but to write to a journal. 16M of cache - split into 32000 writes to single sectors spread over the disk could well take several minutes to write. Slapping it onto a journal would take well under .2 seconds. That's a non-trivial amount of storage though - 3J or so, 40mF@12V - a moderately large/expensive capacitor.

IMHO the best alternative for a situation like that is a storage controller with a battery-backed cache and a hunk of flash NVRAM for when the power shuts off (just in case you run out of battery), as well as a separate 1GB battery-backed PCI ramdisk for an external journal device (likewise equipped with flash NVRAM). It doesn't take much power at all to write a gig of stuff to a small flash chip (Think about your digital camera which runs off a couple AA's), so with a fair-sized on-board battery pack you could easily transfer its data to NVRAM and still have power left to back up data in RAM for 12 hours or so. That way bootup is fast (no reading 1GB of data from NVRAM) but there's no risk of data loss.

Kyle Moffett

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