On 8/16/07, Robert D Oden <roden@xxxxxxxxxxxx> wrote: > After reading many articles which indicate the more disk spindles the > better performance and separating indexes, WAL and data on different > sets of spindles, I've come up with a couple of questions. > > We am planning to buy an external raid sub-system utilizing raid 10. The > sub-system will consist of 12 73GB SAS drives total. > Based on our data requirements we can set this system up using two > different configurations. > > First, we could have two raid sets, one with two drives mirrored for > indexes and the other with four drives mirrored for data. Second, we > could configure as one raid set with six drives mirrored housing both > indexes and data. > > Our environment consists of up to 10-20 users doing a variety of > queries. We have data entry, batch processing, customer lookups and > ad-hoc queries happening concurrently through out the day. > > Almost all queries would be using indexes, so we were concerned about > performance of index lookups with only two spindles dedicated to indexes > (using the first configuration). We thought it may be better to put data > and indexes on one raid where index lookups and data retrieval would be > spread across all six spindles. > > Any comments would be appreciated! > > Second Question: > > Would there be any problems/concerns with putting WAL files on the > server in a raid 10 configuration separate from external raid sub-system? This question comes up a lot, and the answer is always 'it depends' :-). Separate WAL volume pays off the more writing is going on in your database...it's literally a rolling log of block level changes to the database files. If your database was 100% read, it would not help very much at all. WAL traffic is mostly sequential I/O, but heavy. As for splitting data and indexes, I am skeptical this is a good idea except in very specific cases and here's my reasoning...splitting the devices that way doesn't increase the number of random I/O of the data subsystem. Mostly I would be doing this if I was adding drives to the array but couldn't resize the array for some reason...so I look at this as more of a storage management feature. So, I'd be looking at a large raid 10 and 1-2 drives for the WAL...on a raid 1. If your system supports two controllers (in either active/active or active/passive), you should look at second controller as well. merlin ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
