Raid 1

Fri Apr 4 15:23:39 UTC 2008

Thank you for the docs.
I was doing the raid 1 ok.
As Markus said Ubuntu has a problem with raid 1.
This bug was the problem https://bugs.launchpad.net/ubuntu/+bug/133663.
Maybe it will be fixed in Ubuntu version 8.

Karl Larsen wrote:
>   I put things in google and it found:
>
> http://mywheel.net/blog/index.php/software-raid-in-ubuntu/
>
> and I copied the words to my computer for study. It is like this:
>
>
>
> This is a small tutorial to help you getting started with Software RAID 
> in Ubuntu. It was tested on Ubuntu Server 6.06 but it will probably work 
> on Breezy or even on Debian.
>
> Actually, it could possibly work in any GNU/Linux flavour around but I 
> won’t guarantee on that :-)
>
> Please take in attention that you can loose your data! If it happens, 
> don’t complain to me. Follow these guidelines on your own risk.
>
> Why I became paranoid
>
> Five years ago I lost an IBM 80G hard drive that was full of photos, 
> past works and several other important stuff that really mattered to me. 
> I almost cried.
>
> Since then, I became a paranoid with keeping my data safe from harm. I 
> have several machines and there’s a lot of files spawned among them. 
> Call it “Distributed backuping”. Unfortunately, it’s not very useful so 
> I decided I had to have a system that was yet easily usable.
>
> RAID 1 was the answer.
>
> What I bought
>
> To accomplish such, I bought 2x Seagate Barracuda 7200RPM 160GB 8MB 
> Cache. Seagate is well known for is fiability so I didn’t consider any 
> other branch.
>
> Software RAID vs Hardware RAID
>
> Hardware RAID is a must for servers who have a high demand and need 
> serious throughput. Not the case of my home server that’s acting as a 
> fileserver!
>
> Plus, I didn’t have any RAID controller around and sparing €140 on the 
> hard drivers was enough for one day.
>
> I won’t stand my claims (that Software RAID works great for a home 
> server) since you can do it for yourself. Adaptec has some really nice 
> research papers that should how good software RAID can be — although 
> stating that their hardware RAID is better ;-)
>
> Setting up the hardware
>
> I don’t know in depth how the IDE controller works so I couldn’t 
> conclude for myself (nor I had the time to investigate it any further 
> :-) if setting up both hard drives on the same IDE connector (1x Master, 
> 1x Slave) would be faster than having separate IDE connectors (1x 
> Master, 1x Mater). I picked the latter. I’ll wait for some insightful 
> response to this question.
>
> Update
>
> Here’s the response, from Carlos Rodrigues. Thanks Carlos :-)
>
> An IDE channel is a shared bus, so only one drive may be 
> pumping/receiving data at any given time, and some commands lock the bus 
> (try having a CD-Writer and a CD reader on the same channel, and opening 
> and closing the tray on the reader while the writer is recording… 
> instant buffer underrun). Plus, changing directions (write a “read?? 
> command/read data/write a “write?? command/…) is expensive over IDE, so 
> software RAID on a single IDE channel is very bad performance-wise.
>
> On the mean time, you can proceed with any of the approaches and revert 
> it later.
>
> Setting it all from the command line
>
> The system was all set up prior to the Software RAID. Also, I don’t have 
> any X server so all I did was through the command line. Actually, 
> through an SSH session.
>
> The hard work
>
> The first thing I did was checking if both hard drives were being 
> correctly detected on BIOS. They were, let’s move on.
>
> Next, let’s set a partition on each disk and then set its type to Linux 
> RAID. To do such, let’s first figure out which devices the disks got 
> mapped to.
>
> Type $ cat /proc/diskstats. Mine were detected as /dev/hda and /dev/hdc.
>
> To set up a partitition, run fdisk twice, each one for each disk and do 
> the following:
>
> $ fdisk /dev/hdX
>
> Type ‘n’, create a logic partition. Write down the cylinders you used 
> because the partitions on the others disk have to fill the same exact 
> ammount of space. Set it’s type to ‘fd’ by typing t. Finally, save the 
> changes by typing w.
>
> I’ll remember once again than you have to follow this procedure twice, 
> once of earch hard drive.
>
> Now it’s time to create the virtual disk. Make sure mdadm is installed. 
> If it isn’t, I can lend you a hand on that. Just do
>
> $ apt-get install mdadm
>
> Then, fire up the following command
>
> $ mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/hda1 
> /dev/hdc1
>
> Congratulations, your virtual RAID1 hard drive has been successfully 
> created!
>
> Now we need to create a partition with a real file system instead of 
> that virtual Linux RAID you set before.
>
> We’re almost done. Restart the computer.
>
> $ shutdown -r now
>
> The disks are now being synced. You can’t use the virtual disk.. yet. Type
>
> $ watch cat /proc/mdstat and wait until the rsync finishes. In the 
> meanwhile, get a nice cup of coffee of your favourite beverage.
>
> Did it finish? Great!
>
> Format it:
>
> $ mkfs -t reiserfs /dev/md0
>
> Add the new virtual disk entry to /etc/fstab (explaining how /etc/fstab 
> works is out of the scope of this article) and do issue
>
> $ mount -a
>
> Conclusions
>
> You just set a Software RAID on GNU/Linux through the command line. 
> Bottom line conclusions: Linux rocks! :-)
>
> References
>
> http://www.linuxdevcenter.com/pub/a/linux/2002/12/05/RAID.html
>
> https://wiki.ubuntu.com/Raid?highlight=%28raid%29
>
> http://www.howtoforge.com/linux_software_raid
>
> Future work
>
> There’s still a question to be answered. I also welcome any comments 
> correcting grammar, syntax or any other kind of errors.
>
>
> This gets you well on the way to Software Raid 1 and it should work. I 
> got mdadm with no problems. When time permits I will try and get it set 
> up with one HD an IDE and the other a SATA. Not sure how this will work 
> but will find out by doing it :-)
>
> Karl
>
>   