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

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.


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