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
Message-Id: 4F22ECA1.7010002@wildgooses.com
In Reply to: Re: [gentoo-embedded] quickpkg and PKG_INSTALL_MASK by Peter Stuge
1 On 26/01/2012 14:59, Peter Stuge wrote:
2 >> I do have the impression that any block emulating device such as
3 >> SSD are unreliable w.r.t power cuts. I would love to be proven
4 >> wrong though :)
5 > Supposedly, Intel SSDs never report write completed before flash has
6 > actually been updated. Good luck verifying that.
7 >
8 > Everyone else buffers writes. The Samsung 830 series has 256MB of
9 > SDRAM, and their multicore ARM controller handles the magic
10 > buffering. Samsung 830 is built entirely by Samsung from Samsung
11 > parts. All manufacturers besides Intel and Samsung use a mishmash
12 > of components and firmware in their SSD products, and all do magic
13 > buffering.
14
15 I can't find a reference right now, but I am under the impression that
16 the more expensive "enterprise" SSD modules now have some battery backup
17 onboard to allow writes to complete in sudden power down situations? I
18 read recently of one consumer report (probably on Anand tech, but can't
19 find it now...) which had also been fitted with some kind of supercap to
20 handle unexpected powerloss
21
22 (Update, google "SSD supercap" - seems like some of the higher end
23 Sandforce boards have such a thing, and on skimming it is implied that
24 the Vertex3 might have such a thing?)
25
26 I also found this paper which seemed interesting:
27 http://cseweb.ucsd.edu/users/swanson/papers/DAC2011PowerCut.pdf
28
29
30 Seems like it's a rocky road ahead...
31
32 Cheers
33
34 Ed W
35
36
37 P.S. I think this phenomena explains what surely everyone here has
38 experienced, that if you rip out a USB flash drive while it's still
39 writing then every so often the whole drive just disappears (and stays
40 dead)? Also I have killed one CF almost certainly due to a sudden
41 reboot (but it was the design that has since been recalled by
42 PCEngines), and a few others that on reflection might have had a sudden
43 powerdown in a camera or while removing pictures from the camera flash
44 card... Read random amazon reviews of flash drives and there are always
45 a bunch of people who post when their drive totally fails while it's new
46 - again my bet would be many of these would be explained by sudden
47 unplugs during write...