Linux RAID the right way...

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#1 Wed, 12/20/2017 - 00:00
WNYmathGuy's picture

Linux RAID the right way...

Sorry for asking where the links to how to do this are, but is their documentation on this already?

I'm adding a second drive cage to my server and the 8-bays get aggregated in hardware by HP as one logical drive as far as the Ubuntu 16.04 is concerned. The hardware takes sets of 4 drives and makes them RAID-5. The controller makes a pair of RAID-5 groups look like one disk to the OS.

Since I'm RAID safe for any single drive failure in a group, I wanted to install the OS to treat the two 8-bay cages as 2 single drives Striped as RAID-0. I thought it would have gone easier, but it didn't during the Ubuntu install. If anybody knows good instructions for that I'd love to see them.

Tonight I was trying to create a Concatenated or striped RAID using the Webmin interface, and again I thought I could guess my way through, but I'm not sure I know what I'm doing.

Wed, 12/20/2017 - 01:35

I've never used the Webmin Linux RAID module and unfortunately don't have access to it at the moment. I doubt there's official documentation (but there may be). Webmin is basically a GUI for people that already know what they're doing in Linux. You can find numerous How-To guides on creating software RAID in Linux. You would just need to translate the steps to doing it in Webmin. The basic process will essentially be the same otherwise.

Wed, 12/20/2017 - 09:04

if I read it right, you have 2 sets of hardware raids via the HP raid controller. So the OS will see 2 disks, right?

If you then want to raid-0 those, it can be done on the hardware level or the software level. Hardware is dependant on the controller but you just make another virtual drive and add those 2 drives to it. But if you want Ubuntu to handle the raid-0, it would be software controlled. That is doable but not intuitive at install time.

Two ways....

  1. For software raid on the boot/root partition, You can boot off the desktop live cd version of Ubuntu first. It has a tool called gparted. You'll run that and setup the partitions you want on the 2 sets of disks. Set the partition types to linux raid member. Apply, format, continue until its done. Then reboot with the ubuntu server cd and those raid partitions will show up. The raid members will show up in the available partitions list. Setup the raid-0 via the menu at the top, setup you boot or root partitions, mark boot-able. It should then be able to install the OS onto the software raid set.

  2. Or from the ubuntu server cd, you can also setup the partitions. Basically same steps, manually mark disks as raid members. Apply and save. Then go back to the partitioning menu and it should have option near the top to setup raid sets. Once those are setup, back at the main partitioning menu, you should see the new raid-0 set in the partition list. Pick that and setup you boot, root, home partitions. Or at a minimum setup root and let it do the rest. Be sure to mark root or boot as boot-able.

Thats just a basic overview. Here's a detailed guide Although in the guide they setup root and swap on each drive first, which is not needed. Just mark the free space as a raid member, then setup root, swap as needed.

AS far as webmin's raid interface, you wont be able to create bootable raid with that. It wont be able to modify the OS since you're in the OS. But webmin raid pages have no problem setting up raid for other disks. Actually if you create bootable software raid upon install, it can be managed in the raid module. But cant delete or modify because it would be active/in use. But the idea is the same for non OS disks. Create raid type, add partitions or disks to the raid, format, add mount point, create file system like ext4. Will then show up under the mount point. Only quirk is if you want to change/delete a raid set, you have unmount it from the file system page first. Which is totally different page in webmin. Once unmounted, you can then edit/add as raid set again.

Its simpler than it sounds.

Wed, 12/20/2017 - 09:18
Joe's picture

I usually use LVM striping for this kind of thing, these days, but I think the /boot partition still needs to be just a simple software RAID mirror, if using any kind of RAID.

There are decent docs for Webmin's RAID and LVM modules:

But, the RAID features of LVM aren't covered as they're quite new. But, since you're setting it up during installation, this is an Ubuntu question, not a Webmin question. I don't know anything about the Ubuntu installer features for RAID/LVM. I know CentOS has a good LVM setup GUI which handles most of it in a reasonable way.


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Wed, 12/20/2017 - 21:09
WNYmathGuy's picture

Oh... my... Odin! Virtualmin is the best thing that's happened to me in computing in the last decade.

The advice I'm getting is so freaking useful that I'm having trouble putting it into words.

I'm not positive which of the suggested paths I want to take, but the clarity I have now to make a decision is uplifting. I tried the LVM via Webmin tonight because it would be my easiest thing to try tonight. It took me about 5 minutes to undo the bad ideas I tried last night and successfully add the other cage of drives to the main one. It was this sentence "If you began to run out of disk space and wanted to enlarge the filesystem, you could install a new hard disk, add it to the volume group and then enlarge the logical volume to make use of all the new free space!" on this page that did it for me. It was about 8 more clicks to nearly double the size available on my system. I'm thinking that RAID is better than LVM though cause performance, but now I have one successful path to achieve my goals.

I can't help but think that the closer to the hardware that the RAID management happens, the better, and if I stripe I get double the speed. In scotwnw's post, he mentioned a virtual drive done at the controller level. I don't think I can do that. My machine is the HP Proliant DL380 G6. The controller for the second cage is this item; While in the BIOS stages I can F8 into either the internal controller or this optional one, but they seem segregated by every part of the interface. When I F8 into the controller settings I can do a lot; pick the RAID level, decide how I want to pair up any of the 8 drives in a bay, etc. I've never seen anything about combining the two separate controllers into one giant virtual logical set. I'm still just mucking around though. That supplier I got the controller from sent me a bad one. One of the 8 drives is erroneously considered bad (either #1 or #5 depending on switching the wires connecting them). I'm waiting for the replacement controller card before I try the RAID-0 trick; that suggested method done prior to installing the OS.

-- I'm remarkably average

Fri, 12/22/2017 - 03:05

You can use RAID and LVM at the same time. RAID gives you a "physical" drive that the operating system can see. You then add that drive as a physical volume to your logical volume group.

Fri, 12/22/2017 - 22:13
WNYmathGuy's picture

Thank you for making that clear about RAID & LVM. I did have some intentions of doing that. I have set-up all servers with the LVM since a decade ago and never looked back at trying to guess how big to make partitions. The thoughts in my head didn't all make it to the keyboard. I was thinking that if I can get RAID striping across two RAID 5 clusters then install Ubuntu with LVM support, it would run about twice as fast as if I merely used LVM to put the two RAID 5 clusters together after installing Ubuntu.

-- I'm remarkably average

Fri, 12/22/2017 - 22:55

@WNYmathGuy - You are correct on the raid set virtual drives, I didnt understand there where 2 controllers. But why 2 controllers? Get a SAS expander, adding 16,24,48 or more ports to the one controller. Then can setup all kinds of raid sets. That is if that one controller supports expanders. Most main line ones do.

FWIW, I only use hardware raided disks for the OS boot partition. I use linux software raid or LVM for the rest mainly because of the flexibility to change things in webmin with out rebooting.

FWIW#2, LVM in webmin doesn't offer any redundancy. So its best to setup your raid set with redundancy, then LVM on top of that. If ever need to expand LVM. Just add another raid set and LVM on top again.

Thu, 01/11/2018 - 18:58
WNYmathGuy's picture

Finally got my replacement controller card today. Thanks bundles for all the help I got here. I figured out what one of my problems was that it went badly for me in the first place. I had an existing Ubuntu system on existing partitions, and the installer program resists tampering with them. I used the hardware RAID menu in BIOS to delete the existing RAID 5 partitions and recreate them, and voila the job got easy. I have photos of the screens for the next person, but can't post until another day. I'm pressed for time.

-- I'm remarkably average

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