lkml.org 
[lkml]   [2006]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressedby kernelnewbies.org regarding reiser4 inclusion]
    On Mon, 31 Jul 2006, David Masover wrote:

    > David Lang wrote:
    >> On Mon, 31 Jul 2006, David Masover wrote:
    >>
    >>> Oh, I'm curious -- do hard drives ever carry enough battery/capacitance to
    >>> cover their caches? It doesn't seem like it would be that hard/expensive,
    >>> and if it is done that way, then I think it's valid to leave them on. You
    >>> could just say that other filesystems aren't taking as much advantage of
    >>> newer drive features as Reiser :P
    >>
    >> there are no drives that have the ability to flush their cache after they
    >> loose power.
    >
    > Aha, so back to the usual argument: UPS! It takes a fraction of a second to
    > flush that cache.

    which does absolutly no good if someone trips over the power cord, the fuse
    blows in the power supply, someone yanks the drive out of the hot-swap bay, etc.

    >> now, that being said, /. had a story within the last couple of days about
    >> hard drive manufacturers adding flash to their hard drives. they may be
    >> aiming to add some non-volitile cache capability to their drives, although
    >> I didn't think that flash writes were that fast (needed if you dump the
    >> cache to flash when you loose power), or that easy on power (given that you
    >> would first loose power), and flash has limited write cycles (needed if you
    >> always use the cache).
    >
    > But, the point of flash was not to replace the RAM cache, but to be another
    > level. That is, you have your Flash which may be as fast as the disk, maybe
    > faster, maybe less, and you have maybe a gig worth of it. Even the bloatiest
    > of OSes aren't really all that big -- my OS X came installed, with all kinds
    > of apps I'll never use, in less than 10 gigs.
    >
    > And I think this story was awhile ago (a dupe? Not surprising), and the
    > point of the Flash is that as long as your read/write cache doesn't run out,
    > and you're still in that 1 gig of Flash, you're a bit safer than the RAM
    > cache, and you can also leave the disk off, as in, spinned down. Parked.

    as I understand it flash reads are fast (ram speeds), but writes are pretty slow
    (comparable or worse to spinning media)

    writing to a ram cache, but having a flash drive behind it doesn't gain you any
    protection. and I don't think you need it for reads


    >> external battery backed cache is readily available, either on high-end raid
    >> controllers or as seperate ram drives (and in raid array boxes), but
    >> nothing on individual drives.
    >
    > Ah. Curses.
    >
    > UPS, then. If you have enough time, you could even do a Software Suspend
    > first -- that way, when power comes back on, you boot back up, and if it's
    > done quickly enough, connections won't even be dropped...

    remember, it can take 90W of power to run your CPU, 100+ to run your video card,
    plus everything else. even a few seconds of power for this is a very significant
    amount of energy storage.

    however, I did get a pointer recently at a company makeing super-high capcity
    caps, up to 2600F (F, not uF!) in a 138mmx tall 57mm dia cyliner, however it
    only handles 2.7v (they have modules that handle higher voltages available)
    http://www.maxwell.com/ultracapacitors/index.html

    however I don't see these as being standard equipment in systems or on drives
    anytime soon

    David Lang
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2006-08-01 06:59    [W:5.595 / U:0.000 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site