1 file system, 2 drives?
djr at pdconsec.net
Tue Jul 27 06:36:16 UTC 2010
On 27/07/2010 6:54 AM, John Almberg wrote:
> John Almberg wrote:
>>> If you have hardware controller with RAID capabilities, using native
>>> RAID is better, otherwise look towards gvinum or maybe ccd; see also:
>> I've just been reading up on RAID in my Absolute FreeBSD book, and it
>> occurs to me that my client has a SCSI RAID drive chassis that he is
>> using stupidly...
>> It's a 14 bay drive, and he's currently got seven 32G drives stuck in
>> it, configured with RAID-0. This is the original 200G drive I was
>> talking about. It's a few years old.
>> Over the next few years, this guy is going to need lots of storage
>> for his videos.
>> After a bit of reading, I'm wondering if the best idea might be to
>> toss out those 32G drives and replace them with 3 big (say, 300G)
>> drives configured with RAID-5. It sounds to me like a RAID-5 array
>> can be expanded by adding new drives.
>> QUESTION: is expansion normally a matter of just plugging in a new
>> drive? Is the new drive automatically grafted onto the old drives? Or
>> do you have to go through a process like, backing up the data,
>> plugging in the new drive, reformatting the expanded array of drives,
>> and restoring the data.
>> I don't know the brand/model of the RAID drive chassis, but the
>> client thinks it can be switched to use RAID 5. I'm waiting for the
>> technical details, but assuming it can handle RAID-5 for now.
> Answering my own question...
> So its a HP 6402 / 128 RAID controller. From a quick skim of the
> manual, it looks like the controller has to go through an 'expansion'
> process when adding a new drive. This sounds time consuming, but more
> or less automatic -- i.e., handled by the controller.
> Sounds like this might be the best way to go.
It's been a while since I dealt with HP SCSI RAID, but ISTR that you'd
need to install and configure the 3 disks as a RAID 5 set, copy the data
from the 7x36GB array to the new array, (using a temporary mount point,
generally, and dump | restore) switch the mount points across so that
the /videos tree is the new copy, then remove the RAID0 set from the
You may or may not find that the RAID controller changes LUN IDs after a
cold start too, so LUN 1 (new RAID 5) suddenly becomes LUN 0 on the cold
start after the old RAID set is decommissioned and pulled. This is often
accompanied by a heart attack on the part of the person restarting the
After that, though, expansion is a cinch - but it will be quite slow
since it needs to read and write the entire content of all disks. I'd
therefore go as many spindles as you can - 3 disks, 5 disks and 9 disks
are what I recall as being optimal groups for RAID 5.
Also consider that you can supplement the RAIDs with the BSD tools
previously mentioned. Today is 3 x 300GB. Tomorrow add another 3 x 300
(assuming IOPS is OK) and concatenate them to be a 1.8TB "disk" - 2D+P +
PD Consulting And Security
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Email: djr at pdconsec.net
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