(highlandsun)That makes little sense. Just as with RAID, when you use a set of machines instead of a single machine, your MTBF for the total system is inversely proportional to the number of machines. Not to mention the increased administration overhead from managing the larger number of servers, and the painstaking effort to apportion the data to each server and keep the raw data volumes (as well as query volume) balanced as the data grows over time.
MTBF is a number, pure and simple, it's not a guarantee...it's not a precision science. It's affected by many *MANY* different criteria.
I don't see your analogy with RAID, RAID has *many* different types, Raid-0 is a very different animal to Raid-1. They serve very different purposes.
If I buy 4 identical HD's and put 2 into a Raid-0 configuration and 2 into a Raid-1 configuration, have their MTBF's changed? No....what *has* changed is my chances of recovering from a disk going down. Similarly if I run a master LDAP server and two slaves, have their individualMTBF's changed? No....but my time to recover from a "disaster" has drastically changed.
Administration overhead? If you have an LDAP server with a 1TB footprint, you're going to have administration overheads fullstop. I'll take administration
overheads over recovery overheads any day of the week. You can easily hook a number of LDAP slaves up to a master to take over in the event
that the master dies....if you're relying on a single server to perform 1TB of lookups for you then where's your DR plan?QUOTE
There will be 10-20 of these servers located at geographically distributed sites. Certainly not just one. The sysadmin overhead will be bad enough at that. If each site is a farm of smaller servers, the sysadmin cost will skyrocket.
So you will have multiple machines then as I mentioned...
Had you said you have an LDAP server with 1Gb of data I'd agree with you....1TB is another league altogether, that's a big server.....that data is either critical or it isn't...if it isn't critical then you can certainly "cut corners" (as it were), if it's critical then they have to pay the money to keep it critical....
Are those servers serving sub-groups? Do they all carry the same data or are they serving topographically different data?QUOTE
Excuse me? How does a filesystem buffer cache allow you to have consistent reads when it operates in writethru mode? This is such a basic function of any cache, that's not even a worthwhile question.
It's a completely valid question, you gave no information in your original post about exactly what the "transactional backend" was, whether it could be modified by any other processes, whether any jobs run against that backend, etc etc.
This isn't a personal attack against your system, please don't take it as such. I've just seen many systems where people try to build the most powerful machine they can when two or more less powerful systems would actually be cheaper and more effective.
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