I kind of want to set something like this up while spending the least amount of money. I am comfortable enough with Debian/Linux to do most things, but I have never managed anything like this. In the end I want to end up with somewhere relatively safe to store data pretty much in the same way you are, I just do not need 70TiB, and I have no experience with ZFS/hardware stuff/storage.
As far as ZFS on Linux, it still has its wrinkles. I use it because, like you, I'm comfortable with Debian, and I didn't want to maintain a foreign system just for my data storage, and I still wanted to use the machine for other things too. (I actually started with zfs-fuse, before ZFS on Linux was an option.)
So, I don't know. If you just want a box to store stuff on, you might want to just look into FreeNAS, which is a FreeBSD distribution that makes it very easy to set up a storage appliance based on ZFS. FreeBSD's ZFS implementation is generally considered production-ready, so you avoid some ZFS on Linux wrinkles, too.
So, I'd recommend checking out the FreeNAS website, and maybe also http://www.reddit.com/r/datahoarder/ for ideas/other opinions. I do a lot of things in weird idiosyncratic ways, so I'm not sure I'd recommend anyone do it exactly how I have. :)
Plus FreeBSD has a lot of good documentation (and the forums have proven a good resource in the past too) - so you're never going it alone (and obviously you have the usual mailing groups and IRC channels on Freenode).
While I do run quite a few Debian (amongst other Linux) I honestly find my FreeBSD server to be the most enjoyable / least painful platform to administrate. Obviously that's just personal preference, but I would definitely recommend trying FreeBSD to anyone considering ZFS.
I can understand your preference though. I'm not a fan of apt much personally, but pacman is one of the reasons I've stuck with ArchLinux over the years - despite it's faults :)
Thanks for the link, I will take a look there.
You don't need ZFS for this, as cool as it is.
This is probably the number one thing that excites people about ZFS over any other solution, and it's something that isn't really easily implemented on a standard RAID + standard filesystem arrangement, since this sort of functionality depends on the filesystem knowing about the underlying disk arrangement.
"ZFS uses its end-to-end checksums to detect and correct silent data corruption. If a disk returns bad data transiently, ZFS will detect it and retry the read. If the disk is part of a mirror or RAID-Z group, ZFS will both detect and correct the error: it will use the checksum to determine which copy is correct, provide good data to the application, and repair the damaged copy."
I think the pertinent question is: when the filesystem goes to read a 4K block, and one drive's copy of this block in the RAID-1 set is different to its counterpart 4K block on another disk, which one wins?
Honest question: how often to drives silently fail? Drives contain per-sector checksums these days, explicitly to prevent this problem.
Also it may have copies of the data eg raid 1 but does not know which is correct if they differ.
First, in between your monthly/weekly scrubs your disks/controllers will be silently corrupting data, possibly generating errors on multiple devices resulting in data loss depending on raid type. ZFS detects corruption much more quickly.
Second, your traditional raid recovery is to rewriting the entire device to fix a single block. Let's say you're using RAID5 and you're rewriting parity. You get another block error. Oops, now you've lost everything. Since disks have an uncorrectible block error rate of 1 in 10^15 bits, you only need a moderately sized array to almost guarantee data loss. ZFS rewrites corrupt data on the fly.
I'm not trying to argue that mdadm is better than ZFS, just that in this case they pretty much compare the same.
After setting it up, I wouldn't say that it requires any time to manage. Getting it all set up just right, with SMART alerts and capacity warnings and backups and snapshots, all of which I roll myself with various shell scripts, took a long time. Besides that initial investment, the only "management" I have to do is respond to any SMART alerts, add more vdevs as the pool fills up, and manage my files as I would on any other filesystem.
I use the space for just about everything. Lots of backups. I use the local storage on all of my workstations as sort of "scratch" space and anything that matters in the long term is stored on the server. The highest density stuff is, of course, media: I have high definition video and photographs from my digital SLRs, I have tons of DV video obtained as part of an analog video digitization workflow, media rips, and downloaded videos. (I even have a couple of terabytes used up by a youtube-dl script that downloads all of my channel subscriptions for offline viewing, and that's something I doubt anyone would do unless they had so many terabytes free.) I keep copies of large datasets that seem important (old Usenet archives, IMDB, full Wikipedia dumps). I keep copies of old software to go with my old hardware collection. I have almost every file I've ever created on any computer in my entire life, with the exception of a handful of Zip and floppy disks that rotted away before I could preserve them, but that is only a few hundred gigabytes. I scan every paper document that I can (my largest format scanner is 12x18 inches, so anything larger than that is waiting for new hardware to arrive someday), so almost all of my mail and legal documents are on there too.
(I had a dream the other night that someone got access to this machine and deleted everything. Worst. Nightmare. Ever.)
A cloud solution would not have met my use case, since one of the primary needs I have is to be self-sufficient in terms of storing my own data, and I also want immediate local access to a lot of the things on there. I do use various cloud solutions, but only for backup, never as primary storage.
Rolling it myself was definitely cheaper than any out-of-the-box hardware solution I've seen. The computer itself is a Supermicro board with some Xeon middle-of-the-range chip and a ton of RAM, and an LSI SAS card. Connected to the SAS card are two 24-bay SAS expander chassis, which contain the drives, which are all SATA.
I'd say that building something like this would cost you maybe about 4000USD, not counting the cost of the drives. The drives were all between $90 and $120 when I bought them, but of course capacity eventually started going up for the same price over time, so let's say another 3500USD for the drives.