Building your system …

Just had a discussion with a customer who has a 5805 raid card and 7 1tb drives (vendor not an issue here). He originally contacted me asking what the grey ribbon cable on the cables provided with our card were for, but we quickly moved past that to looking at his planned system config.

Note that all drives are 1tb in capacity, and all in a hot-swap backplane. Customer is installing Windows 2008, Exchange (full) and will be using the server as a fileserver as well as an Exchange server. CPU, memory etc were all more than adequate.

Planned spec was:
2 x 1tb drives in RAID 1 mirror for OS (1tb capacity)
4 x 1tb drives in RAID 5 for Exchange and data (3tb capacity)
1 x 1tb drive as hot spare

Problems

1tb for an OS installation is beyond what even Microsoft need these days, and it wastes a fantastic amount of space. Having 4 drives in a RAID 5 is not an issue, except for the fact that Exchange is a database and works much better on RAID 10 than on RAID 5 … the small writes involved in Exchange are not friendly to RAID 5 (or vice versa).

Capacity wise the customer is ending up with 3tb for Exchange and data.

My suggested config for this server is …

1 x RAID 10 on 6 drives for OS – 100gb capacity … this will use 33gb off each disk
1 x RAID 10 on 6 drives for Exchange – 200gb capacity … this will use 66gb off each disk
1 x RAID 5 on 6 drives for data – based on the fact that 1tb drives are generally around 930gb in capacity there will be approxmiately 830gb left on each drive. Making a RAID 5 from 6 of these drives will give around 4tb capacity.

The remaining drive will be a hot spare.

So …

Customer gets

(a) system OS of correct size … which runs faster than it would on a mirror
(b) a fast RAID 10 for his Exchange … which runs a lot faster than it would on RAID 5
(c) a RAID 5 for data which is 4tb in capacity for data (which is a whole lot better than his current 3tb for both exchange and data)

End result … a lot quicker, better utilised system.

This is a classic example of how “knowing” about the capabilities of your RAID card can give you a much better result than just doing the same old things you’ve been doing for the last 10 years.

So what was the grey cable for? That’s another blog if anyone is interested.

Food for thought.

Ciao
Neil

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