[AusNOG] Server/HD Question

[Jake Anderson]

On 14/02/13 15:26, Tony wrote:
> Check the RAID card then, a lot of the ones doing hardware RAID-1 
> don't write any extra meta-data to the disk or mess the disk stucture 
> up, they just write the data to both disks at the same time. This 
> means that you wouldn't have any concerns about what happens if your 
> RAID card fails as either disk can be put into any machine and used as 
> just a normal disk. I haven't played with server hardware for ages, 
> but the entry-level IBM RAID using LSI Logic controllers was like 
> this, two disks, plain mirroring of the disks to each other. Have to 
> be very careful when replacing a disk which one you mirror from/to as 
> the controller doesn't know because there is nothing "special" about 
> the disk that it can identify the "RAID structure" on the disk.
>
>
> Whilst we're tlaking about SSD & SAS/SATA, you can also get RAID 
> controllers that have the option to add SSD as cache disks to store 
> frequently used data on to give some of the benefit of fast access to 
> SSD without worrying about them dropping dead quite so much.
>
>
> Most hardware RAID controllers have a number of features to avoid the 
> issue of having to find the same identical model controller if one 
> dies, but this is a concern. There are several ways to work around 
> this, you can purchase HW maintenance from your vendor and rely on 
> them to have spares for you. If you think RAID controller is a single 
> vulnerability that you don't like, you could purchase two and have a 
> hot spare sitting on your shelf. You could also build in some 
> redundancy at higher layers so that VM's are spread across multiple 
> real machines and recover without downtime if one fails, but you're 
> talking bigger $$ there. Then there is the option of using something 
> like DRDB to give you a RAID-1 set across two machines which is quite 
> interesting:
>
> http://www.drbd.org/
>
>
> regards,
> Tony.
>
<snip>

Thats actually the setup I use
A pair of Dell R210II's for the VM hosts, 24gb ram (buy it from 3rd 
party vendors its still over priced but 1/4 the $2000 dell wants for it)
short computers too, fit in (big) wall mount cabinets.
quad core xeon CPU

bonded gig-E for data network
point to point infiniband connection for cluster communications (it was 
< $100 for the whole setup off ebay for a 10gbps link totally worth it 
for the giggles if nothing else)

pair of 1TB 7200RPM disks
100GB raid1 (mdadm) for /
the other 900 for VM space
I have it set as 2 volume groups one per physical hdd, so mail server on 
one, file server on the other, all the other things spread around evenly.

I use ganeti with KVM for managing the VM's
It handles everything, it sets up DRBD mirroring to the other host and I 
rely on that for "raid".
Does live migration for you all the big boy toys in an open source 
package, used by google.
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