[SOLVED] Software RAID and LVM questions

fettouhi · 2011-04-20 08:34:44

I' running Arch 64 on my machine with RAID 0 using dmraid. I've had this installation running for more than 2 years now without any reinstallation. Originally I ran KDEmod but switched to pure Arch KDE when they became Chakra and discontinued KDEmod. But now it is time to reinstall and I was going to use software RAID instead with LVM because I keep hearing that it is faster. I have 2 500 GB HDD in my quad core machine and I want to set it up with software RAID in the fresh installation. I've been looking at the wiki entry

https://wiki.archlinux.org/index.php/In … AID_or_LVM

and I'm confused how to set it up with raid 0. I was going to make 3 partitions swap, root and home. As far as I understand from the wiki entry. I need to create these 3 partitions on each disk and join them together mdadm. Am I understanding that correctly. I am not interested in getting any redundancy with RAID 1 or 5. I juat want the extra speed increase you get with RAID 0.

Last edited by fettouhi (2012-02-22 17:34:57)

fukawi2 · 2011-04-20 08:45:05

fettouhi wrote:

I was going to make 3 partitions swap, root and home.

I think you're confused about what LVM is exactly.... LVM does not do any form of RAID. If you want RAID, you need a hardware controller, or use dmraid/mdadm.

LVM is for setting up and managing Logical Volumes. You need a boot partition (IIRC, your can't RAID-0 your /boot since grub can't read RAID-0, but I could be wrong) and then you need a partition to be the Physical Volume for the LVM. The Physical Volume(s) are then aggregated to create a Volume Group, which is then divided into Logical Volumes ("partitions") which is what you mount as your root, /home etc.

Normally you would "insert" the RAID between the "partition" and "Physcial Volume" layers. ie, Instead of creating partition(s) to be Physical Volumes, you will create partitions to become members of a RAID array (eg, /dev/md0). This device (md0) would then become the Physical Volume.

Hope this makes sense...

fettouhi · 2011-04-20 09:21:55

well my my motherboard has a raid controller which I'm using at the moment with dmraid. The problem is that dmraid is not supported by grub2, hence I want to switch to software raid instead but I am unsure how to set it up.

fettouhi · 2011-04-20 11:02:23

Just ot clarify the RAID I'm running is what people usually call fake RAID.

fukawi2 · 2011-04-20 12:30:29

You'll want to setup 2 partitions on each drive:
sd[ab]1 = /boot (raid1 this for simplicity)
sd[ab]2 = mdadm software raid partitions

Create the software RAID:

mdadm --create /dev/md0 --raid-level=0 --devices=2 /dev/sda2 /dev/sdb2

Create the LVM physical volume/group/logical volume

pvcreate /dev/md0
vgcreate vg0 /dev/md0
lvcreate --name root --size 8G vg0
lvcreate --name home --size 200G vg0
lvcreate --name vat --size 2G vg0
lvcreate --name swap --size 2G vg0

Repeat (or don't) lvcreate for as many LV's as you want.

fettouhi · 2011-04-20 14:44:10

Thanks for the clarification. Should I turn off the RAID controller in BIOS when I set this up?

fukawi2 · 2011-04-20 23:00:30

fettouhi wrote:

Should I turn off the RAID controller in BIOS when I set this up?

Yes. You are doing all the RAID in software / kernel so all you need the motherboard to do is act as the SATA/PATA controller.

Carlwill · 2011-04-21 12:54:41

I've never got any of that fake to work. Turn it off on your motherboard BIOS. It's generally useless even under Windows which it's intended for. Use 'mdadm'. If you need help with configuring RAID on Arch, let me know. I've done this for some time now and it's very easy now once you understand how to configure it. The Wiki is missing a lot of info and I've yet to update / add info.

skodabenz · 2011-04-21 14:22:30

fettouhi wrote:

well my my motherboard has a raid controller which I'm using at the moment with dmraid. The problem is that dmraid is not supported by grub2, hence I want to switch to software raid instead but I am unsure how to set it up.

Are you sure, AFAIK grub2 1.99~rc1 supports dmraid. Or wait for 1.99~rc2 in the repo.

fettouhi · 2011-07-25 09:34:52

Carlwill wrote:

I've never got any of that fake to work. Turn it off on your motherboard BIOS. It's generally useless even under Windows which it's intended for. Use 'mdadm'. If you need help with configuring RAID on Arch, let me know. I've done this for some time now and it's very easy now once you understand how to configure it. The Wiki is missing a lot of info and I've yet to update / add info.

I'm looking to reinstall my machine after KDE 4.7 hits. What info is the wiki missing on software raid installation?

lilsirecho · 2011-07-25 14:50:03

Perhaps you can follow my posting for installing archlinux on a bootable raid0 setup with CF cards.

Your setup could be HDD's with the same procedure.

My system at present is five CF 16GB devices in raid0, usinf a 100mb partition on one of the devices for boot. The second parttion is the rest of the device. This pattern is repeated on all five drives with the swap designated for the first 100mb of the second device.

During the install procedure, the drives are partitioned, then using ..alt-f2...mdadm is setup for raid0 on the 5 drives using the second parttion of each device in the raid array. After completing the mdadm setup, ...ctl-alt-f1.... to get back to the install sequence.

The mountpoints use swap as device sdb1, root/ as md0 and boot as sda1.

When reaching the bootloader, I selected grub2 and skipped the edit.

I used FTP install of the base and base-devel.

I have used this procedure many times recently producing several combos of CF cards.

My present five card setup provides 306megabytes per second in hdparm and 79 GB of capacity.

It boots in ~13 seconds into xfce4 Desktop.

I use jumnanji for the browser and am in x86_64 mode.

Good luck with your new install.....

edit:hdparm results:

sh-4.2# hdparm -t /dev/sda2 /dev/sdb2 /dev/sdc2 /dev/sdd2 /dev/sde2 /dev/md0

/dev/sda2:
Timing buffered disk reads: 170 MB in 3.03 seconds = 56.03 MB/sec

/dev/sdb2:
Timing buffered disk reads: 202 MB in 3.03 seconds = 66.68 MB/sec

/dev/sdc2:
Timing buffered disk reads: 170 MB in 3.03 seconds = 56.09 MB/sec

/dev/sdd2:
Timing buffered disk reads: 170 MB in 3.03 seconds = 56.03 MB/sec

/dev/sde2:
Timing buffered disk reads: 176 MB in 3.00 seconds = 58.63 MB/sec

/dev/md0:
Timing buffered disk reads: 918 MB in 3.00 seconds = 305.81 MB/sec
sh-4.2#

Last edited by lilsirecho (2011-07-25 15:43:24)

fettouhi · 2011-08-02 14:40:24

I have two 500 GB drives in my machine. I want to partition it with a 100 MB boot partition, 4 GB swap, 30 GB root (/) and the rest is for home (/home). How do I need to partition the install so the end result is what I mentioned before using RAID 0?

lilsirecho · 2011-08-02 17:30:59

My experience with raid0 install is in using CF cards connected via adapters to sataII ports.

The technique should be similar for your HDD's.

In the procedure, when partitioning the drives, calling the first drive sda and the second drive sdb, set up sda with two partitions. This device will be the boot device and should have 100MB in partition#1 and the rest of the drive in partition 2.

Sdb should have a similar arrangement, 100MB swap partition #1 and the rest partition#2 .

After seting up these partitions in the install procedure, select ..alt-f2... and obtain a shell where the following is entered:

mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda2 /dev/sdb2......enter

Then select ...ctl-alt-f1 .... to return to the install procedure. Then do the the next steps therein.

I recommend the arrangement to provide the raid0 for identically partitioned devices.

This arrangement limits swap to 100MB and assumes that sufficient ram is available such that swap isn't encountered during operation.

The use of larger swap may perform in the array but the array will be smaller in size. I have no experience with large swap in raid0.

I assume that the raid array thusly generated will utilize partition2 of each drive as is done in my system of five CF cards arranged as partition#2 raid devices. I obtain 79GB from five 16GB devices and the read speed is 306MB/s.

Good luck................

Last edited by lilsirecho (2011-08-02 17:37:21)

fettouhi · 2011-08-02 19:12:30

fukawi2 wrote:

You'll want to setup 2 partitions on each drive:
sd[ab]1 = /boot (raid1 this for simplicity)
sd[ab]2 = mdadm software raid partitions
Create the software RAID:
mdadm --create /dev/md0 --raid-level=0 --devices=2 /dev/sda2 /dev/sdb2
Create the LVM physical volume/group/logical volume
pvcreate /dev/md0
vgcreate vg0 /dev/md0
lvcreate --name root --size 8G vg0
lvcreate --name home --size 200G vg0
lvcreate --name vat --size 2G vg0
lvcreate --name swap --size 2G vg0
Repeat (or don't) lvcreate for as many LV's as you want.

I there a way with lvcreate to let it use all the space on the raid. Say I create a root partion of 30 gb and at swap of 4 gb. Now I want all the the rest of the space to used for home? Is there a

lvcreate --size all?

alphaniner · 2011-08-02 19:16:24

fettouhi wrote:

I there a way with lvcreate to let it use all the space on the raid. Say I create a root partion of 30 gb and at swap of 4 gb. Now I want all the the rest of the space to used for home? Is there a
lvcreate --size all?

From the wiki:

lvcreate -l +100%FREE VolGroup00 -n lvolmedia

fettouhi · 2011-08-02 21:10:10

alphaniner wrote:

fettouhi wrote:
I there a way with lvcreate to let it use all the space on the raid. Say I create a root partion of 30 gb and at swap of 4 gb. Now I want all the the rest of the space to used for home? Is there a
lvcreate --size all?
From the wiki:
lvcreate -l +100%FREE VolGroup00 -n lvolmedia

Nice, I think I'll try tomorrow to reinstall my machine!

Arch Linux

#1 2011-04-20 08:34:44

[SOLVED] Software RAID and LVM questions

#2 2011-04-20 08:45:05

Re: [SOLVED] Software RAID and LVM questions

#3 2011-04-20 09:21:55

Re: [SOLVED] Software RAID and LVM questions

#4 2011-04-20 11:02:23

Re: [SOLVED] Software RAID and LVM questions

#5 2011-04-20 12:30:29

Re: [SOLVED] Software RAID and LVM questions

#6 2011-04-20 14:44:10

Re: [SOLVED] Software RAID and LVM questions

#7 2011-04-20 23:00:30

Re: [SOLVED] Software RAID and LVM questions

#8 2011-04-21 12:54:41

Re: [SOLVED] Software RAID and LVM questions

#9 2011-04-21 14:22:30

Re: [SOLVED] Software RAID and LVM questions

#10 2011-07-25 09:34:52

Re: [SOLVED] Software RAID and LVM questions

#11 2011-07-25 14:50:03

Re: [SOLVED] Software RAID and LVM questions

#12 2011-08-02 14:40:24

Re: [SOLVED] Software RAID and LVM questions

#13 2011-08-02 17:30:59

Re: [SOLVED] Software RAID and LVM questions

#14 2011-08-02 19:12:30

Re: [SOLVED] Software RAID and LVM questions

#15 2011-08-02 19:16:24

Re: [SOLVED] Software RAID and LVM questions

#16 2011-08-02 21:10:10

Re: [SOLVED] Software RAID and LVM questions

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