I went through this determination when setting up my pool. I decided to go with mirrors instead of raidz2 after considering the following:
1. Drive capacity in my box. At most, I can realistically cram 10 drives in my box and I am not interested in expanding outside of the box. I could go with 2.5 inch drives and fit a lot more, but I don't feel the necessity to do so. That being said, given the historic trend for mass storage drives to become cheaper over time, I have a feeling that I will be replacing drives to expand storage space long before the drives themselves start failing. The added redundancy of raidz2 is great, but I am betting that, barring a poorly manufactured drive, I will be replacing the drives with bigger drives before they have a chance to reach the end of their life. 2. Taking into account the above, it's a great deal easier on the pocket book to expand two drives at a time instead of four at a time. As bigger drives are always getting cheaper, I feel that I have a lot more flexibility with mirrors when it comes to expanding. If you have limitless physical space for drives, you might feel differently. 3. Mirrors are going to perform better than raidz. Again, redundancy is great, but so is performance. My setup is for home use. I want to keep my data safe but at the same time I am limited by cost and space. I think that given the tradeoff between the two, mirrors win. I feel that the chances of two drives in a mirror failing simultaneously are remote enough that I'll take the risk. 4. Again, I'm running this at home. It's not mission critical to me to have my data available 24/7. Redundancy is a convenience and not a necessity. Regardless of what you choose, backups are what will save your ass in the event of catastrophe. Having said that, I currently don't have a good backup solution and how to implement a good backup solution seems to be a hot topic on this list lately. Figuring out how to easily, effectively and cheaply back up multiple terabytes of storage is my number one priority at the moment. So anyways, all things considered, I prefer the better performance and easier expansion of storage space vs my physical space over a relatively small layer of extra redundancy. If you aren't doing anything that necessitates the added redundancy of raidz2, go with mirrors. Either way, if you care about your data, back it up. eric -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
