ZFS: raidz2 with 8 or 10 disks?

The traditional thoughts on ZFS are to have arrays which are a power-of-2 when it comes to number of disks. That means 2, 4, 8, etc. But for raidz1, that would be 3, 5, 9. For my choice of raidz2, it would be 4, 6, and 10.

In the system I’m building up now, I have an 8-port LSI SATA/SAS 9211-8i 6Gb/s card. I can add two more HDD by attaching them to the M/B or to another 2-port SATA card (HighPoint Rocket 620 2 SATA Port PCI-Express) that I have.

I am curious as to what performance changes, if any, will be observed in these configurations:

1. 8 HDD on the LSI card
2. 8 HDD on the LSI card, two on the mother board
3. 8 HDD on the LSI card, one on the mother board, one on the smaller SATA card
4. 8 HDD on the LSI card, two on the smaller SATA card

The system is running FreeBSD 9.1-RELEASE-p4. The test I will do is a PostgreSQL database load and a database dump. I’ll be using PostgreSQL 9.2.4 as installed from ports.

8 HDD on the LSI card

Here is the test I’ll be doing:

$ createdb -E SQL_ASCII -T template0 freshports.org.testing
$ time pg_restore -j 8 -d freshports.org.testing freshports.org.dump.For.Testing
$ time pg_restore -j 8 -d freshports.org.testing freshports.org.dump.For.Testing
$ time pg_dump freshports.org.testing > freshports.org.dump

I’ll be using the plain old pg_dump because it produces the biggest file, as demonstrated in Using compression with PostgreSQL’s pg_dump.

Any comments on this approach?