Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressedbykernelnewbies.org regarding reiser4 inclusion]
From: David Masover
Date: Tue Aug 01 2006 - 01:57:18 EST
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.
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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