Seeking the Holy G(rail)|(raid)

December 31, 2006 5:15 PM

Trying to keep my data around with a minimum of bother, and also looking for a long-term solution. Is there such a thing as a (slowly) growable RAID array?

Ideally, what I want is a system that has 4-6 disk drives in a box. When a disk fails, I pop it out and stick a new one in, and the system automatically heals. This, I know, is standard RAID functionality. (Which number it is, I'm not sure.) But, here's the twist I'd like: When I want to grow the size of the array, I also pop out a disk, and put in a bigger disk. The system automatically re-jiggers the data and I get some fraction of the new space available for my data.

Does something like this exist, or is it possible to set up a system like this? In looking around and asking people, it seems like RAID assumes the same size drives, and doesn't give me the increase in storage space I am looking for. Would something like ZFS or LVM be configurable to produce something like this?

I'm mainly looking for something that would work on either Linux or OS X, but I could live with Windows if that were the best solution.

posted by printdevil to computers & internet (9 comments total)

This can be done in Linux using a combination of the kernel-based software RAID, and LVM, though it's not nearly as seamless as you'd expect (and it's best to use mirrored pairs of drives).
posted by toxic at 6:12 PM on December 31, 2006

Go to www.infrant.com and check out the Ready NAS and their x-raid format. X-raid will grow, but you're still limited by the size of the smallest drive, and only 4 per device.
posted by Steve3 at 6:13 PM on December 31, 2006

I think the ReadyNAS products have this feature.

My experience with configuring my own RAID + LVM solution is that it's not quite what you need. LVM lets you bring new capacity on line, but reconfiguring the RAID to do it one disk at a time is a fussy operation. But, maybe it's changed since the last time I added a disk.
posted by Good Brain at 6:16 PM on December 31, 2006

throwing another vote in for ReadyNAS. Though I sprung for one of the rack-mount ones that I keep in a closet with my router, rather than the ugly "consumer" solutions. (Same features, but I've got no place for an ugly cube like that in my house.)

You can buy them bare and add whatever drives you want. It's not completely effortless, but the closest you'll get at the moment. Down side is that it's limited to 3TB total, though with redundancy and file system overhead you get about half that.

Though you might wait a week or two since I hear that ZFS will likely be included in the next OSX, which would allow the same thing. They might have something worth looking at.
posted by Ookseer at 6:32 PM on December 31, 2006

reconfiguring the RAID [under LVM] to do it one disk at a time is a fussy operation.

Yes, it is. It's significantly easier to do it two matched disks at a time -- but it's still a much more complicated process than it should be, and more complicated than it is with some dedicated NAS units (NetApp got this right over a decade ago, but even their lower-end storevault series is a lot pricey for a home network).

In truth, though, if you're not looking to buy dedicated NAS hardware (the poster did say he wanted something Linux or OSX based), and you're not planning on expanding frequently, it will do the job.

ZFS (in the form of RAID-Z) would also do the job -- but I'm not sure that I'd use Apple's (or anyone else's) first implementation of it (if RAID-Z even goes into 10.5.x). It's just starting to really gain the trust of the (admittedly conservative) Solaris admins that I know, and it's been in the mainline Solaris builds for 2 years.
posted by toxic at 6:54 PM on December 31, 2006

mainline Solaris builds for 2 years

Um, I meant, "The last two mainline Solaris builds", which would be 06/06 and 11/06. Not two years... two revisions. *blush*
posted by toxic at 7:12 PM on December 31, 2006

Thirding or fourthing ReadyNAS from Infrant. I run three of them in various home and office settings and they are awesome, stable well supported boxen.
posted by The Bellman at 7:15 AM on January 1, 2007

Nthing readyNAS. the NV+ is awesome. not cheap, but well worth it. i love how it has an rsync client and can back up all of my machines on its own, on a schedule that i've set.
posted by joeblough at 11:20 AM on January 1, 2007

I've got one of these Highpoint SATA RAID cards, and one of it's features that you're looking for is called "Online Capacity Expansion and RAID Level Migration", which lets you add drives to a RAID 5 and have the array expand. I've used it before, and it does work. Most other "SATA-II" RAID cards have this feature too.

Your hope for being able to expand an array onto new, larger drives is not going to be satisfied. The cheapass route of wanting to throw disparate drives into a single volume is a bad idea. I find that it's a lot better to buy "round" sized drives that exists in a pricing (and manufacturing) sweet spot – namely 250/500/750 GB. With these newer RAID cards (I bought mine a year ago), you can offset the cost by buying a few drives now, and buying more drives for less money later when you actually need the space.

Also, as I've been trying to explain this to people for weeks now (on askMefi and elsewhere), ZFS is not coming in Leopard. The screenshots you saw were fake. I talked to Apple's Developer Relations crew, and they said that the entirety of the ZFS rumor comes from one guy who works at Apple that posted to the ZFS mailing list to see if people might be interested. He is not working on it, he has other shit to do that is more important. There is nobody at Apple working on it for 10.5.0. Time Machine has nothing to do with ZFS — it uses a new HFS+ feature for hard linking to directories, that's it. Don't expect ZFS outside of Solaris anytime in the next year or possibly two, unless Sun goes GPL.
posted by blasdelf at 1:33 AM on January 2, 2007