On 06/06/2010 02:04 AM, Greg Smith wrote:
> u235sentinel wrote:
>
> 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).
Hmmm.. thanks for the wake up. I completely spaced on this. Cache for
writing may be faster but cache for reading the data? Especially with
as much as we're pulling off. Their controllers can do read caching but
I don't think it will make up the difference between the two. I'm
guessing it will be slower even in a raid 10 configuration (the 4540 was
setup with a software raid 10 with the ZFS filesystem).
>
> 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.
Makes sense. The database is only now 2TB and growing still. Currently
we can grow up to around 5 TB. I'm leery of doing this but we'll be
asking for their comparison reports. I'm very curious.
Thanks!