Subject: fast booting & 2*MSL

From: Vernon Schryver <[email-masked]>
Date: Tue, 5 Jan 1999 15:12:11 -0700 (MST)

> From: Rick Jones <[email-masked]>

> All it really takes is switching an IP address from one system to
> another in the event of failure. ...

> Given the pressures on HA in certain markets, I think there is pressure
> to have this detection and failover happen in << TIME_WAIT. I am
> reasonably confident that modulo icky things like DB recovery the
> switchovers are happening < 60 seconds today on a number of platforms.
> Probably much less.

That's a good point.  I but both SGI's and HP's HA offerings switch
in less than 60 seconds at least some times.

] From: rames <[email-masked]>
] To: Vernon Schryver <[email-masked]>
] CC: [email-masked], [email-masked]

] > Which systems have you tested that break that rule?
]
] Embedded systems with TCP/IP stacks in ROM are up in a matter of
] seconds. See, for example, the AMD Net186 Network Appliance demo board
] at
] ...

That's another good point.  One saving grace is that such systems are not
likely to have WWW servers hit by zillions of clients.  They are also less
likely to originate TCP connections, and so can hope their peers will
honor TIME-WAIT and pick new port numbers.  They are also simpler and
could be fixed more easily.  On the other hand, their designers are even
more likely to take short cuts for speed over reliability and to feel
pressures to start working sooner after a reboot.

] From: "Eric A. Hall" <[email-masked]>

] > > Almost every OS that I've ever tested breaks this rule, unfortunately.
]
] > Which systems have you tested that break that rule?
]
] I can get Linux and NT to boot in less than 120 seconds by thinning down
] the number of services in use and using fast gear. I could probably boot
] a Sun box in that same time frame if I tried hard enough.

I'd have to see Redhat 5.1, 5.2, or NT 4.0 boot in less than 120 seconds
to believe it.  Even so, note that I wrote about the de facto standard
2*MSL, which is less than 2 minutes.

]                                                           Big systems
] (VMS, MPE) take longer, but that's mostly due to hardware.

That must involve a definition of "hardware" other than the one I use.

]                                                            Even Compaq
] systems (with their overzealous POST tests) running DOS can take longer
] than two minutes, but the OS doesn't care.

Yes, cold-start tests take far too long on many systems, and have for
decades.  I figure that syndrome is another case of work expanding to fill
the time available.  If power-on diagnostics don't take much time, then
the organization responsible for them loses clout and can suffer.

Vernon Schryver    [email-masked]

---

From: [email-masked] (Alan Cox)
Date: Tue, 5 Jan 1999 23:49:09 +0000 (GMT)

> 2*MSL, which is less than 2 minutes.

Been there, done that. The PC POST test tends to save you but from a warm
restart you can easily have a PC OS rebooting in under 60 seconds. A read
only box like a dedicated web server with the root fs burned on CDROM for
security reasons (hey its cheap and effective) can easily come up in 30
seconds including BIOS time.

There are other cases of fast address change. An ISDN dialup port can
be reused in 3 or 4 seconds.

> the organization responsible for them loses clout and can suffer.

PS/2 8)

---

From: Rick Jones <[email-masked]>
Date: Tue, 05 Jan 1999 14:56:50 -0800

> pressures to start working sooner after a reboot.

There is no guarantee that an embedded web server will have the clients
do the initial FIN is there? I suspect (not that I have any real
data...) that concern for "connection resources" would be such that the
embedded designer would be inclined to be aggressive in closing
connections - ie not make much use of persistent connections where the
chances are better that the client will initiate the close.

Those devices will have a fixed quantity of RAM etc right? I wonder if
they will be written to stop accepting connections when there are no
free control blocks (goodness), or if they will just decided to
prematurely reuse a control blcok in TIME_WAIT (badness).

> That must involve a definition of "hardware" other than the one I use.

Some platforms have hardware (ok, really firmware) that is more
aggressice (conservative?) in start-up self tests than others. MPE
(well, MPE/XL or now MPE/iX) is an OS that runs on PA-RISC which can
have some rather lengthy self-tests for cache and CPU's and such. Newer
systems of such flavor can disable many of these tests (implemented
under pressure from customers looking for faster boot times....) though
it probably still takes at least a couple minutes for such systems to
boot all the way to the point that they are exchanging TCP segments.
Perhaps not a full four minute 2*MSL, but probably more than two
minutes. There is continuing pressure to reduce that boot time further.

rick jones
-- 
today, an ACK takes just as many CPU cycles as a data segment...
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to email, or post, but please do not do both...
my email address is raj in the cup.hp.com domain...

---

From: "Eric A. Hall" <[email-masked]>
Date: Tue, 05 Jan 1999 16:03:05 -0800

> 2*MSL, which is less than 2 minutes.

My Toshiba Tecra 8000 running NT4 wks reboots in 110 seconds without
doing anything fancy. This is measured from hitting "shutdown" at the
login prompt until the login prompt is fully restored (after all
services have started and the disk stops working). The state times ar 20
seconds for shutdown, 25 seconds for system restart (boot menus, etc.),
and 65 seconds for NT to finish loading (and I mean fully finished).

Typically the slow part of the process is the hardware. Scanning the
SCSI bus takes time, for example. Using IDE drives is a lot faster.
There are other areas that can be streamlined. It's not that difficult
to reboot a minimal system in ~90 seconds.

> ] Even Compaq systems (with their overzealous POST tests) running DOS
> ] can take longer than two minutes, but the OS doesn't care.

> Yes, cold-start tests take far too long on many systems, and have for

Compaq boxes are slow on warm start, too.

-- 
Eric A. Hall                                            [email-masked]
+1-650-685-0557                                    http://www.ehsco.com

---

From: "Eric A. Hall" <[email-masked]>
Date: Tue, 05 Jan 1999 16:37:16 -0800

> embedded web server ...

Embedded web servers open a whole 'nother can of worms. HTTP 1.1's use
of persistent connections -- in conjunction with long connections that
are used to transfer many many files (as found on internal web sites in
particular) -- increases the chance that at least one connection willl
eventually reuse sequence numbers. Combined with fast boot times, this
could represent a real problem.

This would be true of any OS that is capable of fast booting, supports
HTTP 1.1 and is used to transfer lots and lots of data.