On Sun, Jan 03, 2010 at 07:53:12PM -0800, Derek Simkowiak wrote: > So, what do you suggest if your client needs a big system that can > survive more than one disk failing?
RAID10. > And, if your client needs a really big server ( > 30TB ), what do you > tell them? Do you tell them "you must double your hardware budget in > order to afford an 8U RAID10 system, as I refuse to build a single-case > 4U RAID6 system"? Probably more than double, and not because the really big server is, well, really that much bigger. I'd want to have a long talk with them about the availability requirements of the data. If this is your home 12-tuner MythTV behemoth, then you have nothing to worry about. If it's a file server or database server serving a few hundred users, you would run out of disk speed long before you'd run out of disk space. Such a huge dataset on such slow disks won't back up overnight. SANs solve this by doing copy-on-write, but it won't restore overnight either. Try a couple days. Would that work for them? Are they OK being billed my consulting rates while I sleep there while it restores? No, more likely if that were really their requirements, they'd need their data regularly replicated to a standby server. Maybe on site, maybe off site. You don't fsck a server that big. It's totally out of the question. You fail over to something else and mess with it outside of production. If a client isn't willing to be realistic about what it costs to do it right, *I do not want them as a client*. > > ...if you're willing to live with 2TB of space. > > I don't understand the argument: "Live with ~half the space and hope > two disks don't fail, because, well, baarf!". Once you have a failure, you'll understand perfectly. In the meantime, I can only say, "I told you so." > I've seen a couple of >600M/sec RAID6 systems, so RAID6 can be Fast > Enough for many applications. If you're doing mostly sequential reads/writes, sure. RAID5/RAID6 come with a fairly large random write performance penalty. This is partially, but not entirely mitigated by controller write caching and battery backup units. > If you need resilience and space more than performance, what beats > RAID6? Again, RAID10. Resilience and performance go hand-in-hand. There's some more exotic combinations such as RAID61, but I don't think we're discussing anything huge enough to make that appropriate. -- Robert Woodcock - [email protected] "Reasonable people adapt themselves to the world. Unreasonable people attempt to adapt the world to themselves. All progress, therefore, depends on unreasonable people." -- George Bernard Shaw
