Re: [PLUG] iSCSI storage appliance(s)

[PaulNM <plug@paulscrap.com>]

On 05/08/2014 01:32 PM, Carl Johnson wrote:
> Who's familiar with any of the NAS distros out there?
> FreeNAS/NAS4Free/NAPP-it/Openfiler/Openmediavault.....etc.?
> 

What kind of hardware do you plan to use? Roughly how much storage do
you plan to manage? Is ISCSI the only thing you'd like to do?

I have more personal experience with FreeNAS/NAS4Free than the others
(except for the Webmin approach I'll mention later).  Actually, to be
precise, I've never used NAS4Free. It's a continuation of older versions
of FreeNAS that I have used, though.

Openfiler appears to be a dead project.  Their last release is ~3 years
old and there doesn't appear to be any real work going on.

Never heard of or used NAPP-it, so can't really comment on it. It
appears to be opensolaris/openindiana based? The site isn't very clear.

Never heard of OpenMediaVault (OMV) either, though it looks *really*
interesting as it's based on Debian.  Not thrilled that they're still
using Squeeze as a base so close to when security support is ending.
Yes, I know Squeeze now has long term support, but that's a *very*
recent change.  Apparently there is a procedure to install OMV on
Wheezy, though.

I've done a project where we used a Debian install with Webmin. This
approach is nice in that there's more flexibility to add other services
down the road. Also, I have a great deal of experience managing Debian
machines, so it's more comfortable for me. Webmin makes it easier for
the less technical people to check up on things and handle simpler
tasks. (I'll call this the WebMin approach.)


> What I'd like to have :
> 1. Flexibility of adding to the total unit capacity with drives of
> different capacities.

FreeNAS can handle this fine, it prefers using ZFS pools. (If you're
familiar with LVM, ZFS is somewhat similar in concept but with more
features.) NAS4Free and NAPP-it should be the same for the same reasons.

OMV and the Webmin approach I mentioned are both linux based.  You can
easily used LVM, RAID, or some combination of both.

That said:

You are aware that RAID/RAIDZ implementations are limited by the
smallest member of their array/volume, right? No matter what solution
you end up using, you'll hit this limitation.  There is unRAID, but
that's not so good redundancy-wise.  ISCSI would be problematic with
unRAID, and you have to pay if you use more than 3 drives.


> 2. Fault tolerance of at least one drive failure; two preferred.

Here's where it gets tricky. ZFS does support setting up a mirror as
well as a few software raid implementations (RAIDZ1/RAIDZ2/RAIDZ3).

What it doesn't support is adding drives to an existing RAIDZ set. Not a
problem if you're starting with all the drives you plan to use, but if
you ever want to add more drives to the RAIDZ:
You'll need to backup the data,
destroy the old RAIDZ,
create a new RAIDZ consisting of the drives from the old one and any new
drives,
restore the backup.

The other option is to add drives in pairs/triplets and make them
separate RAIDZ volumes.

MDADM (Linux RAID) can very easily add drives to existing arrays.
You'll have to expand any LVM volume and filesystem on it afterwards.

> 3. Presenting the storage via an iSCSI target.

Trivial in FreeNAS/NAS4Free. NAPP-it can apparently do this as well. OMV
has a plugin for this, as does Webmin.

> 4. Adding and/or replacing disks without taking the ISCSI target offline.

If the target is a RAIDZ or RAID volume, then yes.

> 5. Admin/management via a web UI (not nearly as important as the other
> four, if I have to use the CLI, so be it.)

All of the examples at the top are geared towards web UI, though many
also let you use a terminal or ssh in.

> 
> Pros/Cons/Suggestions/Thoughts/Tar/Feathers?
> 

The problem with ZFS is that it has many great features, but not all
apply at once. I was looking into it for a major project and got really
excited reading about all the great support it has for adding drives
expanding pools, snapshots, and RAIDZ.  It wasn't until I got into the
details via a test VM that I found out about RAIDZ volumes not being
expandable.

You also need to make sure that whatever OS you use has a version of ZFS
that supports the feature(s) you want to use. I wouldn't mess with ZFS
on linux at all.

Also, ZFS isn't really recommended for 32-bit systems.  You can do it,
but I really don't advise it if you'll be dealing with large amounts of
storage.  Especially if combined with low amounts of RAM.

On the other hand, LVM and Linux RAID are very mature approaches with
easy to use tools.

If a web UI is a lower priority for you, it sounds like this system will
be run by a reasonably technically proficient person. The older I get,
and the more projects I get under my belt, the less I like the
all-in-one or "appliance" approaches.

If you just do a standard install of a distro, you'll get continuous
security updates and a great deal of flexibility.  The downside is it
takes a little more know-how to get things setup. The really nice thing
about Webmin vs some of the other admin interfaces like cpanel/plesk/etc
is that Webmin doesn't really mess with the installed system or make
specialized customizations to it.  It's really just a GUI that edits the
config files for you, while still giving you the option to edit them
yourself. I'm curious where OMV falls on this spectrum.


- PaulNM







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