[Gllug] Hardware comparisons

[James Roberts]

Alain Williams wrote:

> I'm putting together a box for a customer, cost is not the primary
> concern (I'm replacing a 40K AIX box with a dual core AMD based box),
> stability/reliability are highly desirable ... might as well get it
> fast as well.

Although I am no fan of Intel, the current Core-2 based Xeons are faster 
  per pound in almost all circumstances than Opterons. Same for the 
non-Xeons. And they use less electricity. Hurry up AMD.

> There are a few choices, comments please:
> 
> * They wanted SCSI, I had specified SATA ... is SCSI still worth
>   the premium ? We will need a SCSI card for the DAT drive anyway.

Use SCSI. See below.

> * Mirroring. Is this best done by the kernel or through a RAID controller ?
>   I believe that if the kernel sees 2 drives it will do reads in parallel
>   (I believe that computers read more often than they write); it is
>   suggested that using a RAID controller will reduce bus bandwidth (write to
>   controller once which writes to the disks twice) & so make the machine faster.

Use hardware.

The reasons are born out of painful experience:

- SCSI drives are available in exact replacement sizes. This reduces the 
pain of failed disk replacement, especially when using software RAID. 
But for a server you normally need hot-swap and it is cheaper to get 
good hardware for this with SCSI. The sata hot-swap hardware we have 
seen is poop.

- software raid requires much more management. If you want to be able to 
send Fred down with a new drive, then use SCSI. If using software raid, 
then you need to be very careful about the sizes of the volumes so that 
they are easily re-established on a replacement drive that is now 40 
sectors smaller than the original form the same company. Been there. Yes 
in theory all this can be worked around with LVM etc but at some point 
we need to make a profit.

- I don't have any problems with the technical functioning of software 
raid, its fine. However the only times I have lost data it has been on 
software raid.

If none of the above factors are important (in other words, it is not a 
commercial proposition) then by all means use software raid.

> * Memory. Both DDR2 dual channel:
>   One supplier can provide: PC2-4200 (533MHz)
>   The other: PC2-6400 - 800MHz
>   Will the faster memory make a real difference ?

It depends on the cpu and chipset. It may.


Just a note, we have stopped building servers for clients (though we 
'craft custom machines' for special purposes still). By the time you 
cost in a server-class mb, ecc ram, raid controller, array box, drives, 
dual hot-swap psus (we are talking server no?) then the cost of building 
almost always beats the cost of buying and includes a 3-year on site 
service.

We mostly use HP/Compaqs and now Dell. We bought several Dell 
DualCore-Xeon proper servers for 199 each recently on offer. Add a 
3-ware and you have a decent small virtualisation server.

Whatever, ensure that you specify an adequate UPS.

J
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