Re: What exactly is postgres doing during INSERT/UPDATE ?

* Merlin Moncure <mmoncure@gmail.com> [090831 10:38]:

> I agree, that's good analysis.  The main point I was making was that
> if you have say a 10 disk raid 5, you don't involve 10 disks, only
> two...a very common misconception.  I made another mistake that you
> didn't catch: you need to read *both* the data drive and the parity
> drive before writing, not just the parity drive.
>
> I wonder if flash SSD are a better fit for raid 5 since the reads are
> much cheaper than writes and there is no rotational latency.  (also,
> $/gb is different, and so are the failure cases).

The other thing that scares me about raid-5 is the write-hole, and the
possible delayed inconsistency that brings...

Again, hopefully mitigated by a dependable controller w/ BBU...

--
Aidan Van Dyk                                             Create like a god,
aidan@highrise.ca                                       command like a king,
http://www.highrise.ca/                                   work like a slave.