Will Fong put forth on 11/9/2010 6:57 PM: > On 11/09/2010 04:45 PM, Stan Hoeppner wrote: >> The Proliant Dl180 g6 box he has will scale to 192GB RAM in 12 DIMM >> slots, but getting it there gets expensive due to the cost/DIMM at 16GB >> density. Using fairly inexpensive 4GB DIMMS he could occupy 6 of the 12 >> slots for a 24GB capacity. That should be plenty for the requirements >> the OP has described so far.
> There's probably a point where adding a second server will be more cost > effective... Is there really a _need_ to load this all on one host? That dependss on how many concurrent users they eventually have on a regular basis before load stop growing. If they peak at a given maximum concurrent user load, say 2000, a single host system can be setup to meet that load with good performance. If it keeps growing you must scale up by add more processors, RAM, disk, or replacing the box with a larger one, with even more processors, RAM, and disk. Rinse repeat. This is obviously expensive. Scaling out is far more cost effective for very large systems as each node can be less powerful and thus cheaper. The Proliant system the OP is using can be had in the U.S. for less than $1300 USD. Using a local boot disk and a software iSCSI initiator, dozens of such systems could access the same mail store on an iSCSI storage array device via the GFS2 cluster filesystem. Or, using the kernel NFS client and accessing a shared NFS mail store. Here, care must be taken to acquire a high performance NFS filer--a home grown Linux NFS server probably isn't going to cut it. Scaling out with IMAP requires shared mailbox storage, thus this must be planed for up front, bot as an after thought. Now, if you're talking about simply adding new IMAP servers and each one handles mail for a different set of domains, you can sure do that. It's a horrible idea from a resource utilization, load balancing, redundancy, and power consumption standpoint, but it is one possible method. And the upfront costs are less. My main problem with this scenario is you end up with a lot of idle resources. -- Stan
