Nested RAID contraption idea for home Linux file server

L

Langford

[H]ard|Gawd
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Apr 5, 2006
Messages
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I've recently been making upgrades to an old PC, so I could have my own little linux file server at home. My thought was to use a few big disks in a software raid5. Nothing too fancy, and I'll probably just use Ubuntu for simplicity. While looking at the pile of disks of data I intend to transfer over once it's finished, it occurs to me that a couple of them are actually a nice size, although just a quarter of the size of the new disks I purchased. I assume it's still true that I can't just lump the smaller disks in with the new ones in a single raid set and expect it to use all my space, but since I don't believe in a no-win scenario, I've started pondering ways to cheat the rules. Thats were the nested raid thought comes in. The idea is to create two separate raid5 sets, and then connect them as a jbod. The first raid5 set would use the size of my two smaller disks, spread across all the disks, and the second raid5 set would use the remaining space on the larger disks. I'm not especially concerned that the drives may be slightly different speeds, I know the tradeoffs.

Something like this:
Disk 1: ####################
Disk 2: ####################
Disk 3: ####################
Disk 4: #####
Disk 5: #####
Final resulting jbod:
######################################################################

With raid 5 it should be that there is enough redundancy to lose any one drive and keep trucking. Has anyone tried or considered this before, or maybe know a better way to get the results I'm after?

Edit: Considering a plan B also. It would involve 3 sets of raid 5. I little more complicated than the other plan, but both little drives could die and the whole thing would keep on going.

Something like this:
Disk 1: ####################
Disk 2: ####################
Disk 3: ####################
Disk 4: #####
Disk 5: #####
Final resulting jbod:
######################################################################
 
Last edited:
Hmm, why not raid5 the first three, raid1 the last two, and then lvm span the two md sets? You could even raid0 them, but that gives you speed weirdness.
 
Parak said:
Hmm, why not raid5 the first three, raid1 the last two, and then lvm span the two md sets? You could even raid0 them, but that gives you speed weirdness.
Click to expand...
It would be simpler, but I think I'd lose a lot of capacity that way.
 
Make 2 arrays. First one RAID 5 with new discs for data, second one JBOD old discs for backup. Win-Win!
 
It seemed like someone was suggesting you use two drives for the raid zero. I could also be mixing up your old vs new drives.

I think the extra complexity is not worth the redundancy.

How big are the drives? Individually and in aggregate?

What kind of data do you plan on putting on the drives? How do you plan on using them?

Does your Mobo support and kind of raid features?
 
Elf_Boy said:
It seemed like someone was suggesting you use two drives for the raid zero. I could also be mixing up your old vs new drives.

I think the extra complexity is not worth the redundancy.

How big are the drives? Individually and in aggregate?

What kind of data do you plan on putting on the drives? How do you plan on using them?

Does your Mobo support and kind of raid features?
Click to expand...
The big drives are 2TB each and the little drives are 500GB each. There are 4 of the 2TB drives and 2 of the 500GB drives (My diagram shows the wrong number, but I didn't feel like updating it). After the 2TB parity donation I figure it will end up with around 7TB of usable space for my stuff. Some of it is projects and future projects, and some of it is just years of internet fodder. The server will replace piles of external drives, some of which with bad power supplies. The SATA controllers I'm using have cheap-raid, but I don't plan to use that; I plan to just use regular software raid, so it should be easy to migrate it if I ever upgrade the motherboard away from the old one I pulled from my parts shelf. Just an old BP6 in an old beige full tower.
 
How fast do you need the storage to be?

Unless you need at at massive speed (like a huge database) which soft raid isnt going to do, why don't you just get something like a time capsule? With USB you can plug, what 127 TB drives into it and have them all available as network storage?

I realize this makes things a little more complex with more drive letters and needing to keep things organised, porn goes to z:, project x to y: etc, with short cuts and aliasing it isn't that bad.

You can even use drives on the same time capsule as back up for other drives.

Or if you need faster access build a small PC, use external SATA, and/or firewire 800, and/or USB 3 to set up a number of drives. Set up one or two gigabit Ethernet connections and you don't have to worry about windows crapping out, or a single sector going bad in the wrong place wiping everything. Raid five is nice but it is not bullet proof. Maybe the info is old, I have however read some scary stories about losing data with it.

Maybe more work then your thinking or you just like to use raid (why I have a raid 0 in my box) but its an idea.
 
Elf_Boy said:
How fast do you need the storage to be?

Unless you need at at massive speed (like a huge database) which soft raid isnt going to do, why don't you just get something like a time capsule? With USB you can plug, what 127 TB drives into it and have them all available as network storage?

I realize this makes things a little more complex with more drive letters and needing to keep things organised, porn goes to z:, project x to y: etc, with short cuts and aliasing it isn't that bad.

You can even use drives on the same time capsule as back up for other drives.

Or if you need faster access build a small PC, use external SATA, and/or firewire 800, and/or USB 3 to set up a number of drives. Set up one or two gigabit Ethernet connections and you don't have to worry about windows crapping out, or a single sector going bad in the wrong place wiping everything. Raid five is nice but it is not bullet proof. Maybe the info is old, I have however read some scary stories about losing data with it.

Maybe more work then your thinking or you just like to use raid (why I have a raid 0 in my box) but its an idea.
Click to expand...
Thanks for the input, but I've already done the thing where I have tons of separate drives, and this is designed to replace that arrangement. I will no longer have to worry about filling one drive and moving it's contents to another drive, or having another power supply go bad on another external USB drive so that I have to worry about whether my data survived. The hardware planning stage is long since over, I'm a NIC away from having all my parts already, and the idea is to not spend on things I can do for free. it's really not an especially complicated build, just an old big PC that I already own with a bunch of big drives put in it.
 
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