I'm a pretty big user of RAID5 these days, despite a decade where I specialized in storage. There are plenty of reasons for doing RAID6+hotspares+replication (a

I'm a pretty big user of RAID5 these days, despite a decade where I specialized in storage. There are plenty of reasons for doing RAID6+hotspares+replication (and a ton of other fancy choices), but RAID5 nails 99% of the use/problem cases in my book when managed properly. Trust me here, i've seen plenty of raid5 failures... :) RAID5 is one of the best trade-offs in price/perf/availability you can make. Just about no one runs RAID+ on their desktop/laptop because the core storage technology is considered reliable enough that catastrophic failures are rare. Instead good backup hygiene is practiced. For most use cases RAID5 adds a couple digits to your reliability/availability. When properly cared for (scrubbed and smart monitored) the most exciting thing that will happen is you will drop a drive every few ten thousand drive hours, and swapping a replacement in within a day or two, everything will be fine. The cases that manage to take out a well managed RAID5 array, will likely take out just about any other mechanism as well. Having RAID6, RAID10, ZFS or whatever adds additional complexity and won't take care of firmware bugs on the disks, a batch of disks that all blow the bearings within a couple hours of each other, something going horribly wrong with the SATA/SAS controller/expander (think voltage spikes, chassis fires (well i've seen just about everything!)), viruses or bad filesystem bugs. The latter is scary high, a lot higher than most people think, and one of the reasons i'm skeptical of ZFS/BTRFS/etc. But of course, just like your laptop/desktop you need a solid backup/recovery plan, hopefully offsite, multiply redundant and with a reasonable recovery speed. So I strongly encourage everyone to invest and maximize your backup story before you go beyond raid5. Now, there are certain kinds of super critical data, and for those there are fancier solutions (remote replication/etc), but those solutions overwhelmingly aren't as robust as you imagine. Its the old "a plane with two engines has twice as many engine failures" mantra. The more layers of fancy filesystem, replication, deduplicatin, encryption, T10 checksuming, etc you add, the more places that can fail. Which is why you shouldn't even be thinking about them until you have a multivendor offsite (including offline) backup story that can meet you TOS numbers for recovery. It will take exactly 1 building fire to wipe out all that fancy hardware/sofeware, or at least take it offline for days. The last thing you want is the dying breath of your local storage stack to tell the remote one "ok wipe everything" or "here is write for XXXXXXXX sectors....." and trash a big chunk of the remote replicant. Bottom line, RAID5 provides a fair amount of additional assurance against generally unlikely single drive failures. Nothing you can do on a single array/filessytem will save you from all those other bad things that can happen, so backup, backup backup!!!!