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Old 03-10-2010, 03:11 PM
Carlos Mennens
 
Default RAID Configuration & Swap Space

On Wed, Mar 10, 2010 at 3:26 PM, Louis Brazeau <lbrazeau@gmail.com> wrote:
> You are aware that if sda breaks, you loose the /boot partition and
> you can't boot anymore ? I would suggest creating a 100MB /boot
> partition on all 3 disks as a RAID 1 (4GB for boot is over kill IMHO).
> That way you can loose any disk and still be able to boot.

How would I create this via command line across three individual disks?

Do you know that command would look like?
 
Old 03-10-2010, 03:25 PM
Louis Brazeau
 
Default RAID Configuration & Swap Space

On Wed, Mar 10, 2010 at 11:11 AM, Carlos Mennens <carloswill@gmail.com> wrote:
> On Wed, Mar 10, 2010 at 3:26 PM, Louis Brazeau <lbrazeau@gmail.com> wrote:
>> You are aware that if sda breaks, you loose the /boot partition and
>> you can't boot anymore ? I would suggest creating a 100MB /boot
>> partition on all 3 disks as a RAID 1 (4GB for boot is over kill IMHO).
>> That way you can loose any disk and still be able to boot.
>
> How would I create this via command line across three individual disks?
>
> Do you know that command would look like?
>

You can use the RAID/LVM article on the wiki :

http://wiki.archlinux.org/index.php/Installing_with_Software_RAID_or_LVM#Partition_the _Hard_Drives

I used it in the past to setup a few systems with RAID and with or
without LVM. So its your call if you want to use LVM or not.

Also note that the article uses 3 swap partitions in a RAID 1 (total
2GB swap). So you will have to ajust the instructions for your
situation.

Anyway, it will give you a good idea what the commands look like.

--
Louis Brazeau
Informaticien
 
Old 03-10-2010, 03:44 PM
Carlos Mennens
 
Default RAID Configuration & Swap Space

On Wed, Mar 10, 2010 at 4:25 PM, Louis Brazeau <lbrazeau@gmail.com> wrote:
> You can use the RAID/LVM article on the wiki :
>
> http://wiki.archlinux.org/index.php/Installing_with_Software_RAID_or_LVM#Partition_the _Hard_Drives
>
> I used it in the past to setup a few systems with RAID and with or
> without LVM. So its your call if you want to use LVM or not.
>
> Also note that the article uses 3 swap partitions in a RAID 1 (total
> 2GB swap). So you will have to ajust the instructions for your
> situation.
>
> Anyway, it will give you a good idea what the commands look like.

Yes I am very familiar with that Wiki article but find Swap on RAID is
useless, no? For my scenario I was going to do the following and
please correct me if you think this is wrong:

- sda1 = 100MB
- sda2 = 1GB
- sda3 = 300GB

- sdb1 = 100MB
- sdb2 = 1GB
- sdb3 = 300GB

- sdc1 = 100MB
- sdc2 = 1GB
- sdc3 = 300GB

Then:

mdadm --create /dev/md0 --level=1 --raid-devices=3 /dev/sda1 /dev/sdb1 /dev/sdc1

Then mount /boot on /dev/md0. Does that look correct or can I not do
RAID1 on 3 devices? Should I have added '--spare-device=1' to that
command?

Now I would do:

mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sda2 /dev/sdb2 /dev/sdc2

Then mount / on /dev/md1.

Do both commands look OK?
 
Old 03-10-2010, 04:13 PM
Linas
 
Default RAID Configuration & Swap Space

Carlos Mennens wrote:

Yes I am very familiar with that Wiki article but find Swap on RAID is
useless, no? For my scenario I was going to do the following and
please correct me if you think this is wrong:



It is useful if you want to continue running the system even with a
failed disk (without

a restart).
Otherwise, yes. The kernel will distribute stores across swap disk if
they all have the

same priority.

Depending on your bootloader support, you may want to use --metadata=1.0
on /boot to

place raid metadata at the end and make it look like a normal partition.

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Old 03-10-2010, 05:41 PM
Louis Brazeau
 
Default RAID Configuration & Swap Space

On Wed, Mar 10, 2010 at 11:44 AM, Carlos Mennens <carloswill@gmail.com> wrote:
--snip--
> Yes I am very familiar with that Wiki article but find Swap on RAID is
> useless, no? For my scenario I was going to do the following and
> please correct me if you think this is wrong:
>
> - sda1 = 100MB
> - sda2 = 1GB
> - sda3 = 300GB
>
> - sdb1 = 100MB
> - sdb2 = 1GB
> - sdb3 = 300GB
>
> - sdc1 = 100MB
> - sdc2 = 1GB
> - sdc3 = 300GB
>
> Then:
>
> mdadm --create /dev/md0 --level=1 --raid-devices=3 /dev/sda1 /dev/sdb1 /dev/sdc1
>
> Then mount /boot on /dev/md0. Does that look correct or can I not do
> RAID1 on 3 devices? Should I have added '--spare-device=1' to that
> command?
>
> Now I would do:
>
> mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sda2 /dev/sdb2 /dev/sdc2
>
> Then mount / on /dev/md1.
>
> Do both commands look OK?
>

Yes, both look ok to me.

--
Louis Brazeau
Informaticien
 
Old 03-10-2010, 07:27 PM
"David C. Rankin"
 
Default RAID Configuration & Swap Space

On 03/10/2010 08:37 AM, Carlos Mennens wrote:
> I wanted to know if I configure my three identical disks as followed:
>
> - sda1 = /boot @ 4GB
> - sda2 = RAID @ 300GB
>
> - sdb1 = Swap @ 4GB
> - sdb2 = RAID @ 300GB
>
> - sdc1 = Swap @ 4GB
> - sdc2 = RAID @ 300GB
>
> Now when I am done configuring RAID, will Arch Linux show I have 8GB
> of Swap space total under a tool like 'htop' or something like this?
> Will the above configuration work? Or Should I change it?
>

It will probably work, but I would change it. When I mirror a drive, I want
"mirrored" drives (swap & boot included). For me, the purpose behind mirrored
raid is to handle a drive failure. When one occurs, all I want to be required to
do is reinstall grub on the remaining good drive, change fstab and reboot on a
single drive until I get a replacement drive and then rebuild the array.

Yes, I know if you just want disk redundancy for data storage, then you need not
mirror the whole disk. But when swap is no more than 4 gig and /boot is no more
than 150M, with at 750G drive the amount of data loss incurred due to mirroring
a complete drive is less than 1% and for the convenience of instant recovery, it
is worth it.

--
David C. Rankin, J.D.,P.E.
Rankin Law Firm, PLLC
510 Ochiltree Street
Nacogdoches, Texas 75961
Telephone: (936) 715-9333
Facsimile: (936) 715-9339
www.rankinlawfirm.com
 

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