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---
date: 2013-04-07
title: Stop the hate on software RAID
category: Opinions
featured_image: /images/3140gr.jpg
---
I've had a another bee in
my bonnet recently. Specifically, it has been to do with hardware vs
software RAID, but I think it goes deeper than that. It started a couple
of months back with a discussion on [Reddit](https://redd.it/18dp63).
Some of the comments were:
> Get out, get out now.
>
> while he still can..
>
> WHAT!? 60 TB on software raid. Jeezus.
>
> Software raid? Get rid of it.
It then got re-awakened the other day when Matt Simmons (aka [The
Standalone Sysadmin](https://www.standalone-sysadmin.com/blog/)) asked
the following question on Twitter:
<blockquote class="twitter-tweet"><p>
So what are the modern arguments for / against hardware / software RAID?
I don't get out much. #sysadmin
</p>
--- Matt Simmons (@standaloneSA) April 4, 2013
</blockquote>
<script async src="//platform.twitter.com/widgets.js" charset="utf-8"></script>
At the time of writing, 2 people replied: myself and [Chris
Siebenmann](https://utcc.utoronto.ca/~cks/space/blog/). Both of us
basically said software RAID is better, hardware is at best pointless.
First of all, I need to define what I mean by hardware RAID. First, I do
not care about what you are using for your c: drive in Windows, or your
/ partition in Linux. I am talking about the place where you store your
business critical data. If you file server goes down, that is a bad day,
but the business will live on. Lose your business data, then you will be
out of a job (most likely alongside everyone else). Hardware RAID can
thus fall into to categories:
- a bunch of disks attached to a PCI-e card in a big server
- an external storage array. This could be either SAN or NAS, once
again I do not care in this instance.
I am firmly of the opinion that hardware RAID cards should no longer
exist. They are at best pointless and at worst a liability. Modern
systems are so fast that there is no real performance hit. Also
management is a lot easier; if you have a hardware array then you will
need to load the manufacturer\'s utilities in order to manage it. By
manage, I mean to be told when a disk has failed. On Linux, there is no
guarantee that will work. There is a couple of vendors that require
packages from RHEL4 to be installed on RHEL6 systems to install their
tools. Also, they are invariable closed source, will most likely taint
my kernel with binary blobs and generally cause a mess on my previously
clean system. By contrast, using software RAID means that I can do all
the management with trivial little scripts that can easily be integrated
with any monitoring system that I choose to use.
I can understand why people are skeptical of software RAID. There have
been performance reasons and practical reasons for it not to be trusted.
I\'m not going to address the performance argument, suffice to say that
RAID is now 25 years old - CPUs have moved on a lot in that time. I
remember when the first Promise IDE controllers came out, that used a
kind of pseudo-hardware RAID - it was not pretty. The preconceptions are
compounded by the plethora of nasty controllers built in to consumer
motherboards and (possibly worst of all) Window\'s built in RAID that
was just bad.
The thing is, those days are now a long way behind us. For Linux there
is absolutely no need for hardware RAID, even Windows will be just fine
with an motherboard based RAID for its c: drive.
In fact I would say that hardware RAID is a
liability. You go to all that effort to safe-guard your data, but the
card becomes a single-point-of-failure. It dies, then you spend your
time searching Ebay for the same model of card. You buy it, then you
pray that the RAID data is stored on the disks and not the controller
(not always the case). By contrast, if you use software RAID and the
motherboard dies, then you pull the disks and plug them into whatever
box running Linux and you recover your data.
There is definitely a time and place for an external array. If you are
using virtualisation properly, you need shared storage. The best way to
do that, 9 times out of 10, is with an external array. However, even
that may well not be as it seems. There are some that still develop
dedicated hardware and come out with exciting gear (HP 3Par and Hitachi
Data Systems spring to mind). However, the majority of storage is now on
Software.
Let take a look at these things and see just how much \"hardware\" is
actually involved.
The EMC VMAX is a big, big black box of storage. Even the \"baby\" 10k
one scales up to 1.5PB and 4 engines. The 40k will go up to 3PB and 8
engines. Look a little deeper (one line further on the spec sheet) and
you find that what those engines are: quad Xeons (dual on the 10/20k).
The great big bad VMAX is a bunch of standard x86 servers running funky
software to do all the management and RAID calculations.
Like its big brother, the VNX is also a pair of Xeon
servers. Even more, it runs Windows. In fact since the Clariion CX4
EMC has been using Windows Storage Server (based on XP) Move along
to EMC's other lines we find Isilion is nothing more than a big pile of
Supermicro servers running (IIRC) FreeBSD.
Netapp's famed FAS range similarly runs on commodity hardware, OnTAP is
[BSD](https://en.wikipedia.org/wiki/NetApp_filer) based.
The list goes on, Dell Compellent? When I looked at it in early 2012, it
was still running on Supermicro dual Xeons. The plan was to move it to
Dell R-series servers as soon as possible. They were doing validation at
the time, I suspect the move is complete now. Reading between the lines,
I came away with the impression that it runs on FreeBSD, but I do not
know for sure. CoRAID use Supermicro servers, they unusually run Plan9
as their OS. HP StoreVirtual (formerly Lefthand) runs on Proliant Gen8
servers or VMware. In all these cases, there is no extra hardware
involved.
The people that write the MD stack in the Linux
kernel are not cowboys. It has proved over and over again that is
both stable and fast. I have trusted some of the most important data
under my care to their software: for many years the ERP system at
[Snell](https://www.snellgroup.com) has been running on MD devices quite
happily. We found it much faster than the P410 cards in the DL360G5
servers that host it. Additionally, you do not need to load in any funky
modules or utilities - everything you need to manage the devices is
there in the distribution.
ZFS also recommends to bypass any RAID devices and let it do everything
in software, as does Btrfs. With *Storage Spaces* in Server 2012
Microsoft is definitely angling towards software controlled storage as
well.
As with everything in IT, hardware is falling by the wayside in storage.
Modern processors can do the processing so fast that there is no
performance need for hardware in between your OS and the disks any more.
The OS layers (Storage Spaces on Windows and especially MD/LVM on Linux)
are so mature now that their reliability can be taken as a given. With
the management advantages, there really is no technical reason to stick
with hardware RAID. In fact the closer you can get the raw disks to your
OS the better.
As I said at the start, the subject here is software vs
hardware RAID, but my problem goes deeper than that particular argument.
As technology professionals, we are technical people. We need to
understand what is going on under the bonnet - that is our job! It may
be fine for a vendor to pull the wool over a CFO's eyes, but we
need to know what is inside that magic black box, especially when it is
in the spec sheet.