u235sentinel wrote:
> The concern we have is our 4540 has a 2TB database which is working
> great. The server has 48 hard drives (250 gig drives) in RAID 10
> across 6 disk controllers. A couple HBA controllers connected to a
> couple dozen disks may be slower (though dell assures us it will be
> faster than our Sun box).
A Dell system running a PERC with battery-backed write controller will
be faster on database writes than your 4540. Those Sun boxes are
terrible at OLTP style workloads in particular, the types of writes
PostgreSQL does can't be cached by the hard drives in the Sun Thumper
systems. It's possible to bottleneck at ~100 write transactions/second
on them given a particularly incompatible application (I wrote one once,
learned the hard way).
The flip side is that you can absolutely approach 2GB/s on reads on your
Sun system, and I'd expect the Dell one will bottleneck somewhere in the
500MB-1GB/s range no matter how many controllers or drives you put into
it. If your workload is so read heavy that you won't see any advantage
from the write cache you're missing in your Sun box, it's absolutely
possible for the Dell system to be a step backwards. A big Thumper box
will chug away doing big reads against a 2TB database like it's no
problem at all, as you already know.
While I generally dislike Dell, on the hard drive side of things the
current PERC controllers are rebranded LSI Logic ones, and those seem to
have the best performance while keeping reasonable reliability trade-off
available right now. Dell just happens to have one of the best known
formulas for building this sort of server right now.
--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com www.2ndQuadrant.us