Totally agree with everything you wrote, Rick.
I'm not against SANs or VMware at all - I started using VMware years ago
- same for SANs.
I'm just raging against the light of "The Next Big Thing" (TM) - where
various technologies are perceived to be the silver bullet.
We all (I'm assuming) use these various layers of technology - and all
I'm saying is that they are not all things to all people - they are all
things that are very useful in many areas - but - like you - I just
think understanding the technology requires more than simply
comprehending how it works, but also includes understanding where things
are suited, and perhaps where they are not optimum.
That's no indictment of the technology - Citrix as an application
provided isn't all-encompassing in terms of it's suitability, nor is
VMware, nor is SAN storage.
Now of course, improvements in the products and technologies always
improves any weak points - but still, there's no quick-fit for every
scenario.
Neil
_____
From: thin-bounce@xxxxxxxxxxxxx
[mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf Of Rick Mack
Sent: 24 February 2007 05:55
To: thin@xxxxxxxxxxxxx
Subject: [THIN] Re: OT: VMWare ESX 3.x Internal / DMZ networks
on same physical server
Hi Joe,
I hope this isn't interpeted as a religious discussion because
it's not meant to be. SANs have an important role to play in business
and VMWare rocks. SAN disks give you much better throughput than local
hard disks. Period, no argument. SAN storage is good, my customers use
it and I promote it like crazy, in the right places.
BUT we were talking about boot on SAN and the advisability of
using SAN disks as system disks.
The first point to emphasize is that throughput and latency are
different. It's the difference between disk seek time and disk transfer
rate, different units (time vs data/time), different meaning.
I guess I'd like to dispute a couple of the bullet points you
made and maybe concede some stuff as well.
(1) If we're talking system disks (Boot off SAN vs local disks),
SAN disks waste less disk space.
(2) SAN volumes typically have a latenct than local disks. There
are more players between the ball and the goal.
(3) For large data volumes, SANs use the same hard disks we use
as local disks (unless of course you got a really "good" deal and are
using SATA or parallel IDE disks). Same power draw, same heat
production. Since we've got lots of redundancy built in there are extra
power supplies, controllers, fans, cache electronics etc. There's no way
a 72 GB SAN volume could use less power or produce less heat than a 72
GB local disk. How can it when the underlying technology is exactly the
same and you've got more support infrastructure. Also let's not forget
about those spare drives that are in the SAN and powered up just in
case.
(4) HP and IBM as an example are using 2.5 " SAS disk on-board
on blades and stuck in the front of 1RU systems. They don't take up any
extra rack space. SAN disks are in big cabinets and pizza boxes,
generally in their own rack/cabinet.
SANs have much greater hardware redundancy and that means they
ought to be a lot more reliable than a bunch of disks. This is genarally
true, but how often have you had both disks in a mirrored pair fail?
Admittedly these days if a SAN dies it really doesn't matter if
your servers stay up or not but that's not the point.If your SAN dies
because some bozo screwed up a firmware upgrade or decided to re-arrange
the LUNs, you've just discovered that you've got all your eggs in one
basket. If we've used boot on SAN extensively we've got no domain
controller, no terminal servers, no file server, no exchange, no SQL,
nothing.
Even if you've got a fully replicated SAN on your DR site with
up-to-date synchronized data, you can't use the data unless you do a
complete failover to the DR site with all your systems. And if that
isn't an option, how long will it take before you've restored everything
once the SAN is reconfigured and running again?
Don't get me wrong, I don't have a better solution and having
everything on disparate sets of local disks is a total nightmare to
support compared to SAN storage. I'm not biassed against SANs, I just
think it's important to use technology appropriately and as efficiently
as possible. SANs give you tremendous flexibility in data storage, good
redundancy etc but as I've stated above, it comes at a cost. You don't
save power or cooling costs, you don't save space.
Google have shown us that there are other possible architectural
models that don't need SANs. Operating system partitioning has been
around for a long time, and products like Virtuozzo are going to start
eroding the the VMWare market because they're just that much more
efficient. PlateSpin let's you do P2P migrations (not that efficient
yet, but just wait) that can be used for DR redundancy etc. Heck, most
of the time we use pitiful active/passive clustering when you've got
stuff around like Polyserve that makes clustering actually work.
There really is no technology solution that is a 100% fit to all
problems. VMWare isn't the answer to everything, SANs aren't the answer
to everything. We have to stay open-minded and try and use what's
available in the best way possible.
regards,
Rick
I'm going to have to disagree with you and Neil on the
one...
The latency issue with FC vs SCSI is negligible
depending on what your setup is. Sure FC can have higher latency if all
your doing is mapping 2 physical disks (mirrored) to one lun. That's
old school technology. Modern SANs aggregate disks into pools that can
be carved out. Much of SANs and SCSI performance depends on the
hardware used to implement. I've seen 1Gb SAN push a sustained 97MB/s
for reads while a 2 mirrored 10k SAS drives could only sustain 11MB/s
for reads. Extremes perhaps, but real world results.
Yes, SANs are more expensive that local disks, but there
are other considerations be made:
Heat and Cooling costs
Power Draw
Space/Real Estate
Business Continuity and Recoverability
Blades or Pizza Boxes
Just like the blades vs Pizza Boxes debate, each has
it's advantage and disadvantages. However, there is so much more I can
do with a SAN infrastructure that I can do with Local Storage.
Add VMware and BAM! (borrowed this term from Emeril) the
value that can be added to an organization skyrockets. It's no mystery
why VMWare and Virtualization has taken off.
As far a cost effectiveness, that is debatable... When
you factor in Cooling/Power Draw/Business continuity it's hard to argue.
Again, it all depends on what your virtualizing and how important it is
to the business.
If you want a cost effective Virtualization Solution,
then I would suggest looking at Virtuozzo from SWSoft.
Joe
On 2/23/07, Rick Mack < ulrich.mack@xxxxxxxxx
<mailto:ulrich.mack@xxxxxxxxx> > wrote:
Hi Steve,
VMs aside, there are still a couple of significant areas
where SAN disks just don't hack it as a system disk.
The first is latency which can be 4-5 times worse on a
SAN "disk" (overhead of fabric switch and other infrastructure) compared
to local disks. I know that DR etc is a lot easier with SAN disks than
local hard disks, but if you decide to go SAN boot and still want want
real performance then you'd better at least consider using the local
hard disks for paging, spooling and user profiles.
The second issue is price. Even with 72 GB disks where
most of the disk space is wasted, SAN disk space still costs quite a bit
more than RAID mirrored local drives.
I have a suspicion that there will be a time in the near
future when people will start realising that that VMWare isn't nearly as
cost effective as everyone argues. Please don't get me wrong, I love the
idea of VMWare and just wouldn't do without it. It's just that VMWare
isn't really about saving money once we get away from a development
environment.
And until we can overcome disk and network i/o
bottlenecks, having more CPU power to play with just isn't all that
critical. Of course there are things like Vista/Longhorn's flash drive
read/write caching that even things up a bit but what we really need is
the next generation of hard disks that have obscenely large on-board
caches. That'll let them run at close to the interface speeds (eg up to
6 Gb per disk on SASI).
regards,
Rick
On 2/23/07, Steve Greenberg < steveg@xxxxxxxxxxxxxx
<mailto:steveg@xxxxxxxxxxxxxx> > wrote:
Nice! This is one of those mind set changes that
we periodically have to go through. I am going through one right now
with the idea of booting servers off the SAN, in the old days this was
flaky but I have to update my thinking and accept that it works and is
trustworthy!
Steve Greenberg
Thin Client Computing
34522 N. Scottsdale Rd D8453
Scottsdale, AZ 85262
(602) 432-8649
www.thinclient.net <http://www.thinclient.net/>
steveg@xxxxxxxxxxxxxx
--
Ulrich Mack
Commander Australia
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