1 file system, 2 drives?

Gary Gatten Ggatten at waddell.com
Mon Jul 26 21:11:27 UTC 2010

>From my experience (YMMV), most RAID controllers will NOT redistribute the existing data/files onto the newly added drives.  So, if you have a (3) drive RAID5 your file exists on all three drives, as does the parity data.  If you add (2) drives, your original files will not be on the new drives.  New files WILL use all (5) drives.  IMHO it's best to backup the data (twice), create a new volume on the new RAID, and restore the data.  That said, maybe better/newer RAID controllers will redistribute / balance existing data across all drives in the array - I don't know for sure.  Either way, backup your data - twice!  And make sure it can be restored!  Just because the backup app SAYS it's OK, it's NOT OK until it can be successfully restored!

Also, if you go from (7) drives to (3), your I/O may suffer.  Newer faster drives MAY make up the difference, or make up enough of it that it won't impact your client.  Just be aware this is a potential issue.  Generally speaking more spindles = more I/O's / sec.


-----Original Message-----
From: owner-freebsd-questions at freebsd.org [mailto:owner-freebsd-questions at freebsd.org] On Behalf Of John Almberg
Sent: Monday, July 26, 2010 3:31 PM
To: Chuck Swiger
Cc: freebsd-questions at freebsd.org
Subject: Re: 1 file system, 2 drives?

> 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.

Thanks: John
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