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Re: Software RAID (was [OT] 19"/2U Cases)

From: Thomas Goirand <thomas(at)goirand.fr>
Date: Thu Sep 13 2007 - 20:36:51 EDT

Michelle Konzack wrote:

> Am 2007-08-29 14:54:31, schrieb Mike Bird:

>> Software RAID has been reliable for many years. We use software RAID in
>> Etch on dozens of systems ranging from small workstations to terrabyte
>> arrays. When two drives fail in a RAID 5 you'll lose your data - under
>> software RAID yes but also under hardware RAID. There's no need for
>> a 'rebuild drive' because the rebuild starts when the new drive is added
>> with a command such as "mdadm -a /dev/md0 /dev/sda". Simple and fast.

> 
> But you have to shutdown the System to change the drive, since you can
> not change HDD's on the fly using Software-Raid.  Another thing which
> does not work with Software-Raid is hotfix...

Wrong. Hotswap IS possible. Let's say the drive Y with partition Z in the md device X, is to be removed after some smartd warnings:

# Remove the hd from the array:
mdadm -f /dev/mdX /dev/sdYZ
mdadm --remove /dev/mdX /dev/sdYZ
# Stop the drive activity completely:
hdparm -Y /dev/sdYZ

Then unplug the drive, replace it with a new one.

# Copy a new partition table using sfdisk: sfdisk -s /dev/sda | sfdisk /dev/sdY
# Ask the kernel to re-read the partition table: hdparm -z /dev/sdY
# Then add the drive again into the array: mdadm -a /dev/mdX /dev/sdYZ

Done... and quite strait forward! Note that I've tested this only with a modern SATA2 configuration.

Thomas

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Received on Thu Sep 13 20:54:15 2007

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