Text 27066, 145 rader
Skriven 2007-01-19 15:50:20 av Jeff Guerdat
     Kommentar till en text av Gerald Miller
Ärende: Re: duo core - what for?
================================
Gerald Miller wrote:

> So, there is the possibility that the forthcoming "screamer" will be an
> acceptable machine after I retire?  I am greatly relieved by that prospect.

Oh, yeah, mamma!  There's strength in the argument that you should just 
get the cheapest machine you can and replace it every couple of years 
(or as needed) but I prefer to have forward looking expansion capability 
in the first place.  Obviously, "It depends" is a valid modifier.

>  JG> Due to the CPU choice, it's also a nice space heater for the winter
>  JG> months...  ;)
> 
> Hummmm.  That's not the way I want to go!  I got seven fans -- four intake
> and three exhaust.  I had thought about going water cooled, but the price
> quickly modified my thinking.

It's primarily due to to the Xeon CPUs.  Nowadays I'd get a dual core 
something-or-other and have the same benefit with lower power 
consumption and, hence, less heat.  You no doubt have a superior system 
(at least heat-wise) because you're buying current product.  Two years 
ago, dual cores were still being discussed as the next great thing - I 
didn't have a choice.

>  JG> It does take a while to get all the little things converted (mine was
>  JG> from SCSI to SATA) and to determine what the gotchas are so they can
>  JG> be overcome.  For me, it boiled down to 1) getting multiple SATA
>  JG> drives to allow the use of the built-in RAID controller and 2) memory.
> 
> The RAID thingie has me a little confused.  The MB has Intel Matrix Storage
> Technology (RAID 0, 1, 10, 5) and after doing a search at the Wiki site for
> the different RAID "standards", I'm even more confused.
> 
> I think it will be a while before the machine is online, so I will have
> some time to ask more questions about RAID and then make a decision.

The RAID levels are a bear to remember if you don't work with them.

RAID 0 is simple striping - you read or write something and the 
controller splits the job between available drives.  With two drives, 
you get nominally a 2x performance increase since each drive is writing 
concurrently.  Three drives, like I have, gives you 3x the performance. 
  You also get capacity multiplied by the number of drives.  However, 
there's no redundancy so your data is at risk as much as with one drive 
in a normal system.  You need a minimum of two drives.

RAID 1 is mirroring.  What you write on one disk gets written to the 
second automatically.  You can forget about needing to clone a drive for 
backups because it's done for you.  There's a slight performance gain 
because the drive that's ready first is the one to respond.  However, 
there's a loss of capacity since each drive is a duplicate of the other. 
  You can have multiple drives in each part of the array but the $$$ 
overhead is 100% because you need the same number of drives for each 
side of the mirror.  If one side dies, the other can pick up 
automatically (depending on the controller) or you can do some quick 
reconfiguring to do it manually.  Once the bad drive(s) is replaced, 
rebuilding should happen automatically.  You need a minimum of two 
drives but get only the capacity of one.

RAID 10 is generally a combination using BOTH striping (for performance) 
and mirroring (for data protection).  Tends to be expensive due the 
large number of drives needed (a minimum of four drives).

I prefer RAID 5 where striping is used but, like ECC memory, there's 
parity information written.  Since the parity bit has to be written to 
some drive, you effectively have however many data disks plus one.  The 
parity information is actually written across all drives but the effect 
is as if one drive held it all.  There's frequently a small performance 
penalty since the parity information has to be generated and written. 
This scheme will support a single bit (drive) problem.  There are newer 
schemes that support at least 2 bit errors but then you need two extra 
drives.  Minimum of three drives (two data, one parity).  Data is 
automatically calculated with a failed drive so you keep on going but at 
a reduced rate.  Upon replacement of the failed drive, data is 
automatically written to the new drive to bring it up to the level of 
the other drives.  There's also a performance loss during this process 
due to the overhead of calculating the needed data and writing it but 
once it's done, full performance returns.

And then there's hot spares, depending on the size and scope of your 
RAID controller and hardware.  This is a nice to have, but expensive, 
redundancy built in where an unused drive is automatically swapped in 
(logically) for a failed drive.  It has no use other than to be ready in 
case of failure.

Whew!

If you want performance and have some backup strategy to recover from a 
failed disk, RAID 0 is the fastest and cheapest.  Not all cheap RAID 
controllers support RAID 5 so you're left with RAID 0 for data 
protection, which requires 2x the drives.  I chose performance over 
reliability and have backups automatically run by writing to DVD+RW.  No 
need to shut down to backup but there is disc swapping that occurs for 
the full backups (I do full once a month and incrementals weekly).  Your 
paranoia level should dictate your strategy.

> I have two Seagate 320GB SATA drives for the boot OS (both mounted in drive
> caddies so that the boot OS can be cloned)

Right now, you could use either RAID 0 (performance with bothe drives in 
the stripe set) or RAID 1 (mirroring so that data is automatically 
duplicated on both drives).

> If one drive in the array should fail, does the data on the remaining two
> become corrupt?

For RAID 0, yes.  For RAID 1 or 5, no, you're protected although still 
subject to a possible loss of another drive.  Again, your own paranoia 
level should dictate.

> I do like the aspect of the drive speed though...  <g>

Me, too!  That's why I use DVDs for backups with a true backup solution 
so that backups can be run on a live filesystem - no need to shutdown or 
otherwise halt work.  I have it run overnight so there's little to no 
impact.  Full backups require disc swapping but I'm ok with that.

> I'll have to get back to you in regards to the memory.  I'm hoping that 4GB
> should be adequate but I see in another message that there may be some
> limitations on how the memory can be deplored.

Yup - you need the /3GB switch on the OS line in boot.ini or you're 
limited to 2GB for applications.

>  GM>> Now, if I can just keep my wife off the new machine (I'm giving her
>  GM>> the Duron)...
> 
>  JG> I solved that by giving my wife a laptop.  Doesn't need to be fancy
>  JG> for her needs.  (I actually think she's a bit intimidated by the
>  JG> desktop machine - she rarely uses it...)  ;)
> 
> Sorry, a laptop for the wife is not within the budget.

Well, there's some reasonably attractive pricing.  $500 or so should get 
something useful - just postpone a few plans for the new desktop.  Yeah, 
right, like *I* would ever do that...  <smirk>

> The other part of my plan is to transfer my DOS system from the 200MHz box
> to the 500MHz machine.  That should be a snap because on ocassions, I've
> had to swap the drive caddie from the 200 to the 500 box and everything was
> "peaches and cream", only faster.  <grin>

Ah, the simplicity (both positive and negative)...  ;)
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