I ran out of space on my RAID-5 drive, which I built several years ago. At the time, 1TB drives were as large as you could get before the price increased disproportionately to the capacity. I bought 2 “enterprise” grade drives for around $250 each, and a consumer drive for half that. The usable capacity is 2TB because of the redundancy.
I decided I was not going to lose data ever again. Having redundancy against drive failure is one component of this. So, all my photos and system backups are stored there, along with anything else I want to keep safe, including Virtual Machine images.
It turns out that a lot of the space is taken by the daily backups. Even with a plan that uses occasional full backups and mostly incremental backups, they just keep on coming. I also need to better tune the quota for each backup task, but with multiple tasks on multiple machines there is no feature to coordinate the quotas across everything.
Meanwhile, a new drive I installed had a capacity of 3TB by itself. Lots of room for intermediate files and things I don’t need to keep safe. But that’s more to be backed up!
Now I could simply replace the drives with larger ones, using the same Directly Attached controller and chassis space. But there are reasons for looking at Network Attached storage. They even have Drobo NAS units at WalMart now, so it must be quite the mainstream thing now.
Besides future upgradability to more drives (rather than just replace the drives with larger ones again), and better compatibility with different operating systems used in the home, and specialized media services for “smart” TVs and tablets, a compelling reason for me is the reason I’m using a RAID-5 in the first place: to preserve my data. As I’ve noted elsewhere, silent data loss is a bigger problem than generally realized, and it is actually growing. Individual files somehow go bad, and are never noticed until long after you have reused backups from that period.
Direct-Attached storage — simply having the drive on my main PC — limits the choice of file systems. In particular, Windows 7 doesn’t have full support for anything other than NTFS and various varieties of FAT, and new more advanced file systems are only available on a few operating systems as they are not widely used yet.
A file system that specifically keeps data integrity and guards against silent errors is ZFS. When I first learned about it, it was only available for BSD-family operating systems. A NAS appliance installation (using FreeBSD) called FreeNAS started up in 2005. More generally, someone could run a FreeBSD or Linux system that has drives attached that are using ZFS or btrfs or whatever special thing is needed, and put that box on the network.
As I write this, a Drobo 5N (without disks) sells for $550. It reportedly uses a multi-core ARM CPU, and is still underpowered according to reviews. Most 2-disk systems seem to use one of two ARM-based SoC that costs about $30. Now you could put something like the Addonics RAID-5 SATA port multiplier ($62) on that to control more disks at a low price. Most 5-disk home/SOHO NAS systems seem to be based on x86 Atom boards.
Anyway, if you used hand-me-down hardware, such as the previous desktop PC you just replaced with a newer model, you’d have a much more powerful platform for free. Buying a modest PC motherboard, CPU, and RAM for the purpose (supposing you had a case and power supply laying around) could be found for … (perusing the NewEgg website for current prices) … $225.
So basically, if you know what you’re doing (or can hire someone to do it for you for a hundred dollars) you can get hardware substantially more powerful for a fraction of the price.
Being an enthusiast who’s never bought a pre-made desktop PC, it’s a no-brainer for me to put something together from parts, even if it only had the features these home/SOHO appliances that have become so common, even if I don’t re-use anything I have on hand.
But, none of the NAS boxes I see advertised discuss anything like the silent data corruption problem. They don’t say what kind of file system is being used, or how the drives might be mounted on a different system in the event of a board (not drive) failure if a replacement for the exact model is no longer available. I would think that if a NAS had advanced data integrity features then it would feature prominently in the advertising. So, build I must, to meet the requirements.
In future posts I’ll discuss the silent corruption problem at more length, and of course show what I actually built. (I’ve named the NAS server OORT, by the way.)