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    SubjectRe: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressedby regarding reiser4 inclusion]
    David Lang wrote:
    > On Mon, 31 Jul 2006, David Masover wrote:

    >> 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.

    Power supply fuse... Yeah, it happens. Drives die, too. This seems
    fairly uncommon. And dear God, please tell me anyone smart enough to
    set up a UPS would also be smart enough to make tripping over the power
    cord rare or impossible.

    My box has a cable that runs down behind a desk, between the desk and
    the wall. Power strip is on the floor, where a UPS will be when I get
    around to buying one. If someone kicks any cable, it would be where the
    UPS hits the wall -- but that's also behind the same desk.

    > 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

    Does gain you protection if you're not using the RAM cache, if you're
    that paranoid. I don't know if it's cheaper than RAM, but more read
    cache is always better. And losing power seems a lot less likely than
    crashing, especially on a Windows laptop, so it does make sense as a
    product. And a laptop, having a battery, will give you a good bit of
    warning before it dies. My Powerbook syncs and goes into Sleep mode
    when it runs low on power (~1%/5mins)

    >>> 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.

    Suspend2 can take about 10-20 seconds. It should be possible to work
    out the maximum amount of time it can take.

    Anyway, according to a quick Google search, my CPU is more like 70W.
    Video card isn't required on a server, but you may be right on mine. I
    haven't looked at UPSes lately, though. I need about 3 seconds for a
    sync, maybe 10 for a suspend, so to be safe I can say for sure I'd be
    down in about 30 seconds.

    So, another Google search, and while you can get a cheap UPS for
    anywhere from $10 to $100, the sweet spot seems to be a little over $200.

    $229, and it's 865W, supposedly for 3.7 minutes. Here's a review:

    "This is a great product. It powers an AMD 64 3200+ with beefy (6800GT)
    graphics card, 21" CRT monitor, secondary 19" CRT, a linux server, a 15"
    CRT, Cisco 2800XL switch, Linksys WRTG54GS, cable modem, speakers, and
    many other things. The software says I will get 9 minutes runtime with
    all of that hooked up, realistically it's about 4 minutes."

    This was the lowest time reported. Most of the other reviews say at
    least 15 minutes, sometimes 30 minutes, with fairly high-end computers
    listed (and monitors, sometimes two computers/monitors), but nowhere
    near as much stuff as this guy has.

    I checked most of these for Linux support, and UPSes in general seem
    well supported. So yes, the box will shut off automatically. On a
    network, it shouldn't be too hard to get one box to shut off all the rest.

    It's a lot of money, even at the low end, but when you're already
    spending a pile of money on a new computer, keep power in mind. And
    really, even 11 minutes would be fine, but 40 minutes of power is quite
    a lot compared to less than a minute of time taken to shut down normally
    -- not even suspend, but a normal shut down. I'd be tempted to try to
    ride it out for the first 20 minutes, see if power comes back up...

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

    This seems to be a whole different approach -- more along the lines of
    in the drive, which would be cool...
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