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<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";
color:blue'>Thanks Steve, that makes things clear.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";
color:blue'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:
"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;
font-family:"Tahoma","sans-serif"'> mythtvnz-bounces@lists.linuxnut.co.nz
[mailto:mythtvnz-bounces@lists.linuxnut.co.nz] <b>On Behalf Of </b>Steve Hodge<br>
<b>Sent:</b> Tuesday, 16 June 2009 12:30 p.m.<br>
<b>To:</b> MythTV in NZ<br>
<b>Subject:</b> Re: [mythtvnz] File System for RAID-5<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
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<p class=MsoNormal>On Tue, Jun 16, 2009 at 11:54 AM, James Booth <<a
href="mailto:james@booths.net.nz">james@booths.net.nz</a>> wrote:<o:p></o:p></p>
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<p><span style='font-size:10.0pt;color:blue'>I’m starting to lean towards
RAID1 or RAID10. There is one thing that I am not clear on with RAID1, maybe
someone can help me here.</span><o:p></o:p></p>
<p><span style='font-size:10.0pt;color:blue'> </span><o:p></o:p></p>
<p><span style='font-size:10.0pt;color:blue'>I understand the RAID is created
out of partitions, as opposed to physical drives. Does this mean I can divide 3
x HDD’s into 6 equal partitions, and then set up a RAID-1 solution that
mirrors each partition on another partition that resides on a separate physical
drive? ie I don’t need an even number of disks for a mirrored system? If
so, how does adding in more disks work? </span><o:p></o:p></p>
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<p class=MsoNormal style='margin-bottom:12.0pt'>You can build mdraid volumes
out of partitions or whole drives. So yes, you can split each drive into two
partitions and then setup 3 RAID1 volumes from pairs of partitions on different
drives. When adding more disks you can degrade some of the arrays and use the
resulting spare space to create a bigger array with the new drive. Eg, you'll
start with the following (drives are 500GB, labeled A, B, C, partitions are
250GB):<br>
Array 1: A1 B2<br>
Array 2: B1 C2<br>
Array 3: C1 A2<br>
<br>
Say you get a new 500GB drive, 'D'. If you're willing to stick to 250GB arrays
(rather than reconfiguring to 500GB arrays) you can add the new drive while
ensuring that you always have two copies of everything. Partition the new drive
into two 250GB partitions. Then add partition D2 to array 3 (so array 3 has 3
copies of the data). Once the array has sync'd you have:<br>
Array 3: C1 A2 D2<br>
<br>
Now remove partition A2 from array 3. Finally set up a new array using D1 and
A2. So you end up with:<br>
Array 1: A1 B2<br>
Array 2: B1 C2<br>
Array 3: C1 D2<br>
Array 4: D1 A2 (empty)<br>
<br>
If you're not worried about maintaining two copies of everything during the
process you can do this: create a new array out of the new drive D. Set it up
with a missing copy. Remove C from arrays 2 and 3. Set up another array with
drive C and a missing copy. At this point you have:<br>
Array 1: A1 B2<br>
Array 2: B1 -<br>
Array 3: - A2<br>
Array 4: D - (500GB)<br>
Array 5: C - (500GB)<br>
Copy everything from arrays 1, 2, and 3 to arrays 4 and 5 however you like.
Then delete arrays 1, 2, and 3 and add drives A and B to arrays 4 and 5. Once
they sync you'll have:<br>
Array 4: D A<br>
Array 5: C B<br>
<br>
Expanding a (mdraid) RAID10 is not so easy but I recommend it if you're not
likely to expand often as the performance can be much better. You can set it up
so that a single filesystem is striped across the 3 or 4 drives without needing
LVM on top.<br>
<br>
Cheers,<br>
Steve<o:p></o:p></p>
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