Reading this article has had me thinking - http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/ - which basically says RAID1 (equivalence) is better than RAID5, and I fully understand the argument. It's about tradeoffs of storage efficiency vs failure tolerance.
What I found myself specifically wondering though is does it make more sense to mirror drives (or vdevs) or to simply mirror entire servers instead with some kind of failover in place?
If i'm going to have 16 drives lets say, should I throw 8 drives in two separate towers and sync the towers, or should I throw them all in one with a single RAID controller letting that do the managing? What are the pro's and con's each way?
Some are obvious to me - 2 servers will take a bit more power, but have a bit more protection under many incidents - an exploding PSU can wipe out every drive in your system, that shouldn't happen with a good PSU, but the point is it contains failure better. Also more drives in one system tends to demand more expensive equipment - cheaper 'commodity' clusters could have financial advantages since the parity calculations and such demands more of the cpu side to work at larger sizes (paying less for disks matters less if I need 128gigs ram instead of 2gigs ram on some simple mirrored cluster) maybe for diminishing returns.
From either the software support side, or just the general 'engineering' side, are there strong reasons not so obvious to go one way or another?
Assume backups ARE being properly done and that RAID 1/5 are not a replacement for backups. Just fault tolerance to insure one dead disk doesn't stop the day's work or cause immediate loss of the day's data.
What I found myself specifically wondering though is does it make more sense to mirror drives (or vdevs) or to simply mirror entire servers instead with some kind of failover in place?
If i'm going to have 16 drives lets say, should I throw 8 drives in two separate towers and sync the towers, or should I throw them all in one with a single RAID controller letting that do the managing? What are the pro's and con's each way?
Some are obvious to me - 2 servers will take a bit more power, but have a bit more protection under many incidents - an exploding PSU can wipe out every drive in your system, that shouldn't happen with a good PSU, but the point is it contains failure better. Also more drives in one system tends to demand more expensive equipment - cheaper 'commodity' clusters could have financial advantages since the parity calculations and such demands more of the cpu side to work at larger sizes (paying less for disks matters less if I need 128gigs ram instead of 2gigs ram on some simple mirrored cluster) maybe for diminishing returns.
From either the software support side, or just the general 'engineering' side, are there strong reasons not so obvious to go one way or another?
Assume backups ARE being properly done and that RAID 1/5 are not a replacement for backups. Just fault tolerance to insure one dead disk doesn't stop the day's work or cause immediate loss of the day's data.
I have a series of questions but don't just want to spam the board with them. I get ideas in my head then either try to refine them or look at alternatives/are even better ideas than what I think makes sense out there? So over the months i'll be slowly reading more, and hammering out my decisions on major things first whenever I think I have enough information to choose. But it's always possible to still change those decisions if new information I didn't have before comes my way until I commit to buying stuff. I try to list in every post "what I think I will do and why" hoping people will shoot holes in my idea if there are flaws.
