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Old 12-24-2001, 12:02 AM   #1
system
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Software RAID vs Hardware RAID


Concerning RAID 1 only!

Someone told me that Linux's software RAID was less reliable than hardware RAID. I am trying to build a RAID array only for reliability. It is going to be for low performance file serving so performance is not a big issue, only reliability. Is software RAID any less reliable then hardware?

Also, if I have two RAID 1 partitions, is it possible to mount one of the partitions and use it as a standard partition? I would want to be able to do this in case of some kind of failure in the RAID setup or failure to recover from drive failure. Could I access the good disk if for some reason the RAID driver wasn't functioning or I wanted to go back to using only one disk, non-RAID?
 
Old 12-24-2001, 10:46 PM   #2
DavidPhillips
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I have a system with soft RAID 1


when a disk fails you do not need to do anything it will continue to run on the good disk. If the machine is rebooted it will boot on the good disk and run normally.

you must replace the bad disk and add it to the RAID array to regain the RAID array.

If you have a spare disk in the system it will be used when one fails automatically.

This only protects against hard drive failure. It does nothing for the file system to protect against loss or corruption of data due to lockups or power failure.

You need to look into a journaling file system like ext3 for that.


Last edited by DavidPhillips; 12-24-2001 at 10:49 PM.
 
Old 12-24-2001, 11:30 PM   #3
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Thanks.

Can you use ext3 with software raid? Also, can you convert an ext2 filesystem to ext3?
 
Old 12-25-2001, 09:11 PM   #4
DavidPhillips
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yes and yes

if you are using an kernel prior to 2.4.16 then you need to install it as a module.

It is now in the kernel so you can add support for it, It is listed as experamental, so I don't know if it's a great idea, but you can still load the module.

if it's a module the / partition needs an initrd file, initial ram disk.


if you have it, run tune2fs -j to create the journal file and change ext2 to ext3 in /etc/fstab

LABEL=/ / ext3 defaults 1 1
LABEL=/boot /boot ext3 defaults 1 2
LABEL=/home /home ext3 defaults 1 2

this command will show if it is working

cat /proc/mounts

/dev/root / ext3 rw 0 0
/dev/md1 /boot ext3 rw 0 0
/dev/hdb5 /home ext3 rw 0 0


or this the md0 and md1 are raid..

cat /etc/mtab
/dev/md0 / ext3 rw 0 0
/dev/md1 /boot ext3 rw 0 0
/dev/hdb5 /home ext3 rw 0 0



Last edited by DavidPhillips; 12-25-2001 at 09:16 PM.
 
  


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