[wplug] NAS Appliance recommendations

[Patrick Wagstrom]

There are several ways that Drobos deal with running out of disk space.
Most of which I've found to be pretty satisfactory:

1) There is a plugin for explorer and finder that lists the true amount of
space left.  Under linux there is the command "drobom" that can be used to
monitor your space left.

2) When you're running out of disk space, the drobo will illuminate its case
with a yellow light by the smallest drive -- indicating that drive needs to
be replaced.

3) as you get really close to running out of space, drobo exponentially
slows downs writes to the disk.  So, at 97% you take a small hit in write
speed, but at 99% it's REALLY REALLY SLOW.  I've tried and have never gotten
to the point where the drobo says it's out of disk space.  It just slows
everything down a lot.  I guess this is so other users will notice how slow
it is and pester you until you actually upgrade the drive.

This issue of is common with most systems that allow on the fly expansion.
The main reason is because most filesystems don't tolerate expansion without
unmounting them first, however, that can be a real pain because you then
need downtime.  It's a tradeoff here.

On Sat, Aug 22, 2009 at 9:33 PM, James O'Kane <jo2y at midnightlinux.com>wrote:

> I can understand the reason to tell the os you have a fixed sized
> partition, but having a volume that isn't backed my real disk seems scary to
> me. I'm assuming that you'll get just a write failure if you exceed the
> physical space?  And if you're writing to both of them it could be either of
> the that fails first?  Is there a software way of determining the amount of
> physical space remaining?
>
> On Aug 19, 2009 12:04 PM, "Patrick Wagstrom" <patrick at wagstrom.net> wrote:
>
> I've had no problems running a ext3 on my drobo.  Everything works just as
> you would expect it.  The caveat is that it's a little harder to get volume
> sizes in excess of 2TB.
>
> Here's how the drobo typically works:
>
> power on drobo, insert bunch of drives, boom 2tb drive shows up on
> operating (regardless of actual storage size).  This is something that is
> typical of almost any logical storage device because operating systems don't
> often deal with drives changing their size on the fly.
>
> If you add in more drives you'll have an additional drive just show up.
> So, if you've got 3x1TB drives and 1x500GB in your drobo, you'll have 2.5TB
> of usable space. This will show up as /dev/sdc1 and /dev/sdc2 as both being
> 2TB drives.  You can fill either one with 2TB of data, as long as the other
> doesn't have more than 500GB. Furthermore, you can change on the fly,
> balance with 1.25TB on each, whatever.
>
> With NTFS and HFS+ you can specify up to a 16TB volume size.  You can do
> the same for EXT3, but it's a little more complicated.
>
> --Patrick
>
>
> On Wed, Aug 19, 2009 at 1:04 PM, G.Pitman <gpitman at gmail.com> wrote:
>
>> > > We do have a guy in house that has been using a Drobo for over a year
>> and is pretty happy. > > I...
>>
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