Raid 1+5+0?

[K.J.]

Hi, I'm pretty new to the Raid game, but have recently enjoying the comfort of knowing my data is at the very least protected from hardware failure (my really important data is still backed up offsite).

This leads me to my question. Is it possible to stripe together Raids of different types? i.e. Can I create a Raid 0 out of a raid 1 and raid 5?

The reason is, I have 4 disks. Two are 1 TB and two are 300 GB. I currently have it set up as 1+0. However, since speed and redundancy are not that important and disk space is become a premium, I'd like to maximize the storage space while still having fault protection of 1 disk. So, is it possible to create a Raid 5 of 4x300GB partitions and a Raid 1 of 2x700 GB partitions and then a raid 0 of the resulting 900GB and 700GB partitions?

Also, I'm not trying to raid 0 for speed concerns, just the ease of load balancing the disks because you would theoretically be able to treat the raid 0 as a single partition of 1600 GB.

Thanks!

[pricetech]

First of all, you don't have a RAID 5. You have two RAID 1s based upon what you've described.

Even if you could do what you want, you're only gaining 300 gigs. I don't think it would be worth the trouble of dumping all your data and trying to set it up.

Stick with 1+0 unless you plan to purchase a 3rd drive to make a RAID 5 array.

[ratcheer]

I agree with pricetech, you need RAID 1+0. First, you mirror two pairs of disks, then you create a RAID 0 stripe across the two LUNs. This gives high performance (RAID 0) and complete redundancy (RAID 1).

Tim

[K.J.]

I think you misunderstood a bit. I know I don't have Raid 5 right now. Right now I have 1+0. What I wanted to know is its possible to create a create a single unit (either raid 0 or linear) out of a raid 5 and a raid 1.

It's for a DVR storage box. If it's not possible I'll just be out the extra 300 GB and I'll just start saving for an additional drive.

Thanks for the help.

Edit:

Also, performance is not an issue since it doesn't take much to read/write a single video file. The issue is it needs to be all one storage unit so I don't have to manually move files when one fills. Right now I'm solving that issue with raid 1+0.

[CharlesA]

Probably just run a RAID-5 setup with as many disks as you need.

Oh and make backups! RAID is not a substitute for good backups.

[K.J.]

Probably just run a RAID-5 setup with as many disks as you need.
Raid-5 alone does not solve my problem because my disks are of different sizes (2x1000 GB and 2x300 GB). Which only allows for 4 disk 900 GB raid 5. I could then create a Raid 1 out of the 700 GB left over on each 1000 GB disk. I want to know if there is a way to make these two raids act as a single unit.


Oh and make backups! RAID is not a substitute for good backups.
I appreciate your help, but I'm not looking for a lecture. In fact, I even mentioned in my first post that I back up all of my important data offsite. The purpose of THIS set up is only to protect my DVR from hardware failure.

[CharlesA]

Raid-5 alone does not solve my problem because my disks are of different sizes (2x1000 GB and 2x300 GB). Which only allows for 4 disk 900 GB raid 5. I could then create a Raid 1 out of the 700 GB left over on each 1000 GB disk. I want to know if there is a way to make these two raids act as a single unit.

They would have to be used independently, as you cannot mount 2 partitions to the same place.

As for creating a RAID-5 then a RAID-1 with the extra space, maybe try mdadm.

I wouldn't recommend having 2 arrays on the same disk, but that's just me.

[K.J.]

I know you can't mount two devices to the same point, but is it possible to make a raid out of raid arrays? Thanks.

For example, is the following valid:
mdadm --create /dev/md2 --level=0 --raid-devices=2 /dev/md0 /dev/md1

[CharlesA]

I really don't know, since I haven't used mdadm since I run hardware RAID5.

Maybe try it out in virtualbox to see if it'll work? I don't know.

[K.J.]

I really don't know, since I haven't used mdadm since I run hardware RAID5.

Maybe try it out in virtualbox to see if it'll work? I don't know.

Oh, I didn't think of that. I'll try that when I get a chance and report back.

EDIT:

As an aside, I just got a free PC from work that was going to get trashed. It's a 3.0 ghz P4 with HT. Not amazing, but it certainly blows the P3 out of the water. I just moved the drives and the gigabit ethernet card over (didn't need the SATA card, as the mobo had 4 SATA ports). WOW! I LOVE Linux/Ubuntu!! So easy. I expecting to boot up and have to at the very least fix my grub, rebuild the RAID array, and rename the Ethernet port to eth0, but it all worked perfectly on boot. No errors, just booted right up like I didn't change a thing.

Plenty of horsepower to saturate by 4 megabit uplink now. I'll let ya'll know if I get around to trying out the RAID array of RAID arrays thing.

[fjgaude]

A couple of years ago I tried making an array out of three other arrays using mdadm and it worked just fine. No issues.

[K.J.]

It worked fine in a VM I tested. However, I decided that my current setup (Pentium III) can't handle the overhead as it already pegs the CPU at 100% on HTTPs transfers. I'll hopefully be upgrading soon.

[Krupski]

I know you can't mount two devices to the same point, but is it possible to make a raid out of raid arrays? Thanks.

For example, is the following valid:
mdadm --create /dev/md2 --level=0 --raid-devices=2 /dev/md0 /dev/md1

Yes, you can make RAID arrays out of RAID devices. Don't see the point though... especially since you want to RAID together drive partitions. Having 2 or 3 partitions on the same PHYSICAL drive does not give you RAID redundancy.

Your best bet would be to ditch the 300 GB drives, buy one more 1TB drive and make a 2TB RAID-5 array with the three physical drives.

[K.J.]

Yes, you can make RAID arrays out of RAID devices. Don't see the point though... especially since you want to RAID together drive partitions. Having 2 or 3 partitions on the same PHYSICAL drive does not give you RAID redundancy.

Your best bet would be to ditch the 300 GB drives, buy one more 1TB drive and make a 2TB RAID-5 array with the three physical drives.

The purpose of the top level raid is striping, not redundancy. All the data is still (at least) RAID-5 redundant. It's also important to note that the purpose of the RAID-0 in this setup is NOT performance, and a simple concatenation would suffice.

Disk 1 [300 GB, sda1] [700 GB, sda2]
Disk 2 [300 GB, sdb1] [700 GB, sdb2]
Disk 3 [300 GB, sdc1]
Disk 4 [300 GB, sdd1]

md0 -- RAID 5 [900 GB, (sda1, sdb1, sdc1, sdd1)]
md1 -- RAID 1 [700 GB, (sda2, sdb2)]
md2 -- RAID 0 [1600 GB, (md0, md1)]

If that helps to explain. Although, I do agree with you. I probably won't bother. I'll just wait until I have $100 for another 1 TB drive and a SATA card.

[ratcheer]

It worked fine in a VM I tested. However, I decided that my current setup (Pentium III) can't handle the overhead as it already pegs the CPU at 100% on HTTPs transfers. I'll hopefully be upgrading soon.

Dern, I thought my Pentium 4's were old!

Tim