Gentoo Archives: gentoo-embedded

From: Ed W <lists@××××××××××.com>
To: gentoo-embedded@l.g.o
Subject: Re: [gentoo-embedded] quickpkg and PKG_INSTALL_MASK
Date: Fri, 27 Jan 2012 19:09:27
In Reply to: Re: [gentoo-embedded] quickpkg and PKG_INSTALL_MASK by Peter Stuge
On 26/01/2012 14:59, Peter Stuge wrote:
>> I do have the impression that any block emulating device such as >> SSD are unreliable w.r.t power cuts. I would love to be proven >> wrong though :) > Supposedly, Intel SSDs never report write completed before flash has > actually been updated. Good luck verifying that. > > Everyone else buffers writes. The Samsung 830 series has 256MB of > SDRAM, and their multicore ARM controller handles the magic > buffering. Samsung 830 is built entirely by Samsung from Samsung > parts. All manufacturers besides Intel and Samsung use a mishmash > of components and firmware in their SSD products, and all do magic > buffering.
I can't find a reference right now, but I am under the impression that the more expensive "enterprise" SSD modules now have some battery backup onboard to allow writes to complete in sudden power down situations? I read recently of one consumer report (probably on Anand tech, but can't find it now...) which had also been fitted with some kind of supercap to handle unexpected powerloss (Update, google "SSD supercap" - seems like some of the higher end Sandforce boards have such a thing, and on skimming it is implied that the Vertex3 might have such a thing?) I also found this paper which seemed interesting: Seems like it's a rocky road ahead... Cheers Ed W P.S. I think this phenomena explains what surely everyone here has experienced, that if you rip out a USB flash drive while it's still writing then every so often the whole drive just disappears (and stays dead)? Also I have killed one CF almost certainly due to a sudden reboot (but it was the design that has since been recalled by PCEngines), and a few others that on reflection might have had a sudden powerdown in a camera or while removing pictures from the camera flash card... Read random amazon reviews of flash drives and there are always a bunch of people who post when their drive totally fails while it's new - again my bet would be many of these would be explained by sudden unplugs during write...