LinuxQuestions.org
Share your knowledge at the LQ Wiki.
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Software
User Name
Password
Linux - Software This forum is for Software issues.
Having a problem installing a new program? Want to know which application is best for the job? Post your question in this forum.

Notices


Reply
  Search this Thread
Old 05-21-2014, 07:32 PM   #1
xmrkite
Member
 
Registered: Oct 2006
Location: California, USA
Distribution: Mint 16, Lubuntu 14.04, Mythbuntu 14.04, Kubuntu 13.10, Xubuntu 10.04
Posts: 554

Rep: Reputation: 30
Mdadm Raid 1 - Do I have three raids or one raid with 3 partitons?


What is the recommended setup?

Ubuntu alternate 14.04. I want to setup a raid 1 with 3 partitions: one for boot, one for swap and one for data.

Should I create one raid and then partition the /dev/md0 into 3 partitions (which the installer can't do), or should I create 3 separate raid devices: md0, md1, and md2?

Which is recommended and why?

-Thanks
 
Old 05-22-2014, 06:45 AM   #2
chrism01
LQ Guru
 
Registered: Aug 2004
Location: Sydney
Distribution: Rocky 9.2
Posts: 18,369

Rep: Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753
How many physical disks do you actually have?
If you only have 2, create /dev/md0 and partition into 3: "/" (inc boot), swap, "data".

The point of RAID is to protect you from HDD failure, so creating 3 'devices' for one pair of disks doesn't really make sense.

(I need hardly add that RAID is NOT a backup system.)

HTH
 
Old 05-22-2014, 09:15 AM   #3
xmrkite
Member
 
Registered: Oct 2006
Location: California, USA
Distribution: Mint 16, Lubuntu 14.04, Mythbuntu 14.04, Kubuntu 13.10, Xubuntu 10.04
Posts: 554

Original Poster
Rep: Reputation: 30
Ya, two disks. My point is how do I partition the raid into 3 partitions from the ubuntu alternate installer? All I see that I can do is create three equal partitions on each drive and create 3 raid devices.

I'd like to just create one big raid device and partition it into 3 partitions...but I must be missing something because I can't seem to figure out how to do that in the installer.
 
Old 05-22-2014, 10:44 AM   #4
EDDY1
LQ Addict
 
Registered: Mar 2010
Location: Oakland,Ca
Distribution: wins7, Debian wheezy
Posts: 6,841

Rep: Reputation: 649Reputation: 649Reputation: 649Reputation: 649Reputation: 649Reputation: 649
https://help.ubuntu.com/community/In...n/SoftwareRAID
 
Old 05-22-2014, 11:16 AM   #5
xmrkite
Member
 
Registered: Oct 2006
Location: California, USA
Distribution: Mint 16, Lubuntu 14.04, Mythbuntu 14.04, Kubuntu 13.10, Xubuntu 10.04
Posts: 554

Original Poster
Rep: Reputation: 30
So this sort of proves my point:

According to those instructions, you have md0, md5, and md6 - 3 raid devices.

If I make one big raid partition, then boot up a live ubuntu dvd, install mdadm and then open gparted. I can then partition the md0 raid 1 "device" into 3 partitions.

So there's obviously two ways to do this. Why does the installer want 3 raid devices? I think it'd be simpler to just worry about one raid device and have that have multiple partitions.

If I go with hardware raid, that is what would happen: The hardware raid utility would create one raid 1 using the two drives. Then ubuntu would make the partitions. So you'd have only one raid device but multiple partitions. Is software raid different for this?


What am I missing?
 
Old 05-22-2014, 12:09 PM   #6
EDDY1
LQ Addict
 
Registered: Mar 2010
Location: Oakland,Ca
Distribution: wins7, Debian wheezy
Posts: 6,841

Rep: Reputation: 649Reputation: 649Reputation: 649Reputation: 649Reputation: 649Reputation: 649
You have to read more carefully it says different.
It said for 2 disk raid setup partition disk 1 then setup raid.
 
Old 05-22-2014, 01:03 PM   #7
jlinkels
LQ Guru
 
Registered: Oct 2003
Location: Bonaire, Leeuwarden
Distribution: Debian /Jessie/Stretch/Sid, Linux Mint DE
Posts: 5,195

Rep: Reputation: 1043Reputation: 1043Reputation: 1043Reputation: 1043Reputation: 1043Reputation: 1043Reputation: 1043Reputation: 1043
Most tutorial explain that first the partitions on the hard disks are created (sda1, sda2, sdb1, sdb2...) and each partition set is raided. So sda1+sda2 becomes md0, sdb1+sdb2 become md1.

Chrism01 proposes to first create one partition of the size of the hard disk, and then partition md0 into mda0, mda1.. etc.

Are mda0, mda1 correct device names anyway?

What would be the advantage of that approach?

jlinkels
 
Old 05-22-2014, 01:09 PM   #8
xmrkite
Member
 
Registered: Oct 2006
Location: California, USA
Distribution: Mint 16, Lubuntu 14.04, Mythbuntu 14.04, Kubuntu 13.10, Xubuntu 10.04
Posts: 554

Original Poster
Rep: Reputation: 30
Ok, so on one of my computers I setup the raid outside the installer and then went to the installer and partitioned my md0 device into 3 partitions.

It installed and boots just fine. Now when I boot up and check mdadm I have one raid device to monitor. Simpler than monitoring 3 raid devices.

On one of my servers I did the same idea, but have 4 drives and partitoned 2 raid 1's and one raid 5. So that server has 3 raid devices. The ubuntu installer basically would have led me to setup 6 raid devices.

Why do they go for more raid devices when you can easily do it in less devices? I only want to have one device so that if a drive goes bad and I put in a new one, I only run one sync command.

I guess my question now is why do they do it this way? It looks for certain that you are forced this route by just using the installer.
 
Old 05-22-2014, 03:05 PM   #9
EDDY1
LQ Addict
 
Registered: Mar 2010
Location: Oakland,Ca
Distribution: wins7, Debian wheezy
Posts: 6,841

Rep: Reputation: 649Reputation: 649Reputation: 649Reputation: 649Reputation: 649Reputation: 649
Quote:
Why do they go for more raid devices when you can easily do it in less devices? I only want to have one device so that if a drive goes bad and I put in a new one, I only run one sync command.
If you have 2 devices it is already synced, jusr take the bad drive out. Also how can you sync a bad drive if you can't mount it?
 
Old 05-22-2014, 11:11 PM   #10
xmrkite
Member
 
Registered: Oct 2006
Location: California, USA
Distribution: Mint 16, Lubuntu 14.04, Mythbuntu 14.04, Kubuntu 13.10, Xubuntu 10.04
Posts: 554

Original Poster
Rep: Reputation: 30
We're getting off topic.

1. Why are there two options for raid: multiple raids or one raid with multiple partitions?

2. Why does ubuntu's alternate installer only allow the second option?


Those are really my main questions. I am able to make either option work, but I want to make sure I am choosing the industry standard, tried and true method. If anyone can chime in on this one, please do.
 
Old 05-23-2014, 08:12 AM   #11
chrism01
LQ Guru
 
Registered: Aug 2004
Location: Sydney
Distribution: Rocky 9.2
Posts: 18,369

Rep: Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753Reputation: 2753
1. because you can ... basically in Linux, choice is king - seriously
2. no idea: never touched Ubuntu

In Centos I'd do a Custom Setup at the Partitioning stage of the install.
Something like http://www.linuxtopia.org/online_boo...id-config.html

If its a new (added) disk set, I'd use the cli eg
http://www.tuxradar.com/answers/280
 
Old 05-23-2014, 02:15 PM   #12
xmrkite
Member
 
Registered: Oct 2006
Location: California, USA
Distribution: Mint 16, Lubuntu 14.04, Mythbuntu 14.04, Kubuntu 13.10, Xubuntu 10.04
Posts: 554

Original Poster
Rep: Reputation: 30
1. I like choice - that's why I choost linux
2. That is the same example as ubuntu's. Three raids, not one raid with partitions inside it.
 
  


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off



Similar Threads
Thread Thread Starter Forum Replies Last Post
Recover mdadm RAID after failure during RAID level change Caetel Linux - General 1 11-07-2013 10:38 PM
Why can't I mount this md0 raid? (mdadm and software raid) cruiserparts Linux - Software 35 01-05-2013 03:35 PM
Broken raid 5 (11 drives in mdadm) -- data recovery/raid reconstruction needed -- ple jml48197 Linux - Server 4 07-27-2010 12:57 PM
Dell/Intel ICH7 soft-RAID and mdadm raid-level mistake PhilipTheMouse Linux - General 0 03-14-2009 05:59 PM
RAID mdadm - Sending E-Mails on RAID Failure? rootking Linux - General 1 12-25-2007 03:59 AM

LinuxQuestions.org > Forums > Linux Forums > Linux - Software

All times are GMT -5. The time now is 11:57 PM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Open Source Consulting | Domain Registration