1 file system, 2 drives?

Rich rl001 at pacbell.net
Tue Jul 27 00:57:29 UTC 2010

From: Gary Gatten <Ggatten at waddell.com>
Cc: "freebsd-questions at freebsd.org" <freebsd-questions at freebsd.org>
Sent: Mon, July 26, 2010 1:41:19 PM
Subject: RE: 1 file system, 2 drives?

>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.


>>Generally speaking more spindles = more I/O's / sec.

and more chance for failure. After a certain point adding more drives to a RAID0 
stripe doesn't buy you anything because the first one is ready for the next 
command before you get very far down the line.

-----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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