On 01/15/2014 08:29 AM, Derek Yarnell wrote:
On 1/15/14, 9:20 AM, Mark Nelson wrote:
I guess I'd probably look at the R520 in an 8 bay configuration with an
E5-2407 and 4 1TB data disks per chassis (along with whatever OS disk
setup you want). That gives you 4 PCIE slots for the extra network
cards, the option for a hardware raid controller, and some expansion
options if you want to add more disks. It's not the densest chassis and
I've never tested performance on it, but it's a fairly straightforward
setup with no expanders to worry about and a cheap/fast CPU.
Dell recently will sell now a R720xd with a pure LSI card in it (you
will need to ask). This is important that the PERC controllers do not
support JBOD mode and really for Ceph you don't want a hardware raid
controller. They currently give me a hard time about trying to mix and
match SSDs though on the 12 bay back-plane which is not a technical
problem but a Dell problem. However you can get two flex bays in it
which they allow you to put SSDs in. So you can get 12 4TB drives and 2
100G eMLC drives in 2U.
That's good to know that they will sell LSI controllers in the R series
now! JBOD vs RAID has some nuances. As far as I know, LSI controllers
basically disable cache when put in JBOD mode (as opposed to something
like Areca that keeps it enabled), so you give up a lot when you run in
JBOD mode. With SSD journals (that have a supercap) this is much less
of an issue as you don't have to worry about journal writes and data
writes competing on the same disk. With journals on disk, it appears
that controllers with WB cache can help quite a bit. In this scenario
you'd use single disk RAID0 arrays. This is actually what DreamHost does.
Thanks,
derek
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