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I want to set up a NAS at home for sharing music, movies etc. I have four hard drives: 2 x 500GB, 1 x 1.5 TB and 1 x 2TB. is it right that I cannot set up a RAID 5 like this? what alternatives are there?

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migrated from serverfault.com Mar 30 '11 at 9:35

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Please read our FAQ as this question is clearly more appropriate for our sister site superuser.com, that said I'm pretty sure someone will suggest Drobo's product line for this. –  Chopper3 Mar 30 '11 at 9:35
    
Buying recommendations aren't really welcome here, so I'd take that out of your question if your real problem is finding out if a RAID 5 is possible. –  slhck Mar 30 '11 at 9:39

5 Answers 5

You can set up a RAID 5 with these drives, but it would be a complete waste. The RAID will be 3 times the capacity of the smallest drive, so 1.5TB.

What would be nice would be if you could create a JBOD of a 500GB and the 1.5TB drive to make 2TB and then mirror that (RAID 1) with the 2TB drive. That would give you a 2TB mirror and one 500GB drive left over.

I don't know if RAID subsystems can actually do this though, but I am just experimenting with ZFS to see if I can do it. I know ZFS will let you just JBOD all the disks together, but that leaves you open to the whole disk pack becoming unusable if only one disk fails.

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That config is certainly doable - I have a Linux server with a 120GB drive striped with a 320GB one and then this is mirrored (RAID 1) with another 120+320GB pair to give 440GB of storage - all IDE drives too in a soon-to-be-retired server. Based on my experience, I'd be tempted to use a basic install of Linux to setup the storage and then use serviio as the media server: serviio.org –  Linker3000 Mar 30 '11 at 12:39
    
ok... this sounds like a hack job. what about that drobo thingee? –  elluca Mar 30 '11 at 22:19

If you wanted to use RAID, you could do the following:

You could set up a 500GB partition on each of your drives, and RAID-5 across them.

Obviously this will leave you with unused space on the two larger-capacity drives. You could then do RAID-1 to use up another 1TB on the two larger disks.

This would leave you with 0.5TB of unused space on your largest drive, which you could then use as a rather excessive OS/swap partition - if you didn't care about redundancy for this.

Alternatively, as Chopper3 suggested, you could use something like Drobo to allow you to slap in disks of all shapes and sizes. But your disks wouldn't be readable by other systems in future if your Drobo failed.

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RAID across partitions on a single drive? That's pointless. The point of RAID is to protect you if a device fails. In your case if a device fails you will lose multiple partitions and the RAID will be dead and gone, along with all the data. –  Majenko Mar 30 '11 at 9:47
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If you read my answer, I suggested one partition on each of the drives. –  Steve Mayne Mar 30 '11 at 9:55
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Ah yes - slightly vague wording but I see what you mean –  Majenko Mar 30 '11 at 10:05
    
ok, i am quite interested in drobo. what are the downside of it? by "if it fails" you mean that if it breaks i have to buy a new one to recover my data? well, i can live with that. i think the drobo fs is going to suit my needs best. any comments on that model? and have a look at this: Synology they claim: "eliminating the need to have hard drives of identical size". does this also do what i want? –  elluca Mar 30 '11 at 23:47
    
another question: in a demo video of drobo the demonstrator can only choose between 1 & 2 TBs of partition space. has this changed? are there donwsides of the tool being that simple? or do i have the same features as with a usual NAS which i can access via the command line or so? EDIT: ah, i got it. you only set the maximum capacity... what a nice feature! can you modify that later on? –  elluca Mar 31 '11 at 7:52

Ars Technica has a good write up on the Drobo here: http://arstechnica.com/business/raising-your-tech-iq/2011/03/drobo-review-1.ars Drobo's are pricey but allow you to group drive of various sizes using their own "raid-ish" scheme. The two biggest issues I have had with NAS boxes is some devices have their OS on one of the drives, if it fails then you have to do some really arcane stuff to get the OS back on the replacement drive. Second issue is rebuilding a array for a failed drive is very time consuming. For any NAS device that shouldn't be your only backup, it should be seen as a convenient access point.

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you want to tell me that i have to get another backup of my future NAS? why? if my house burns down i guess i will have other problems ;) –  elluca Mar 30 '11 at 23:52
up vote 0 down vote accepted

Use unRAID.

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I suggest not doing RAID for a home NAS. There's no reason to do it other than to be able to tell people you have a RAID. "I run my home NAS in a RAID 5, and so I'm an uber-geek and you should think I'm cool because of it."

Why waste the space? Do you really run mission critical data at home that need seven nines of live availability? You're wasting space and potentially creating slower NAS performance.

Instead, use the space you have and do dual incremental backups at night. You'll get better performance, better data security, and the ability to restore files from backup. If your primary drive fails, swap it out for last night's backup. It's like 10 minutes to do it if you take a lunch break in the middle.

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Given how long it takes to restore even 500GB of data and how cheap drives are, I must disagree here. Doing a RAID5 is rarely useful for a home user, but a couple RAID1 sets would be very helpful –  Zoredache Apr 28 '11 at 23:38

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