lkml.org 
[lkml]   [2008]   [Jan]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck)
    Theodore Tso wrote:
    > On Wed, Jan 16, 2008 at 09:02:50PM -0500, Daniel Phillips wrote:
    >> Have you observed that in the wild? A former engineer of a disk drive
    >> company suggests to me that the capacitors on the board provide enough
    >> power to complete the last sector, even to park the head.
    >>

    Even if true (which I doubt), this is not implemented.

    A modern drive can have 16-32 MB of write cache. Worst case, those
    sectors are not sequential which implies lots of head movement.

    >
    > The problem isn't with the disk drive; it's from the DRAM, which tend
    > to be much more voltage sensitive than the hard drives --- so it's
    > quite likely that you could end up DMA'ing garbage from the memory.
    > In fact the fact that the disk drives lasts longer due to capacitors
    > on the board, rotational inertia of the platters, etc., is part of the
    > problem.

    I can tell you directly that when you drop power to a drive, you will
    lose write cache data if the write cache is enabled. With barriers
    enabled, our testing shows that file systems survive power failures
    which routinely caused corruption without them ;-)

    ric




    \
     
     \ /
      Last update: 2008-01-18 00:23    [W:3.224 / U:0.440 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site