Bristol Digest, Vol 592, Issue 3

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Today's Topics:

1. Linux Raid (Huw Morgan)
2. Re: Linux Raid (Martin Moore)
3. Re: Linux Raid (Keith Edmunds)
4. Re: Linux Raid (Alex Butcher)


----------------------------------------------------------------------

Message: 1
Date: Thu, 5 Mar 2015 16:24:01 -0000
From: "Huw Morgan" <huw@cleevemill.net>
To: <bristol@mailman.lug.org.uk>
Subject: [bristol] Linux Raid
Message-ID: <003b01d05760$ca2dcae0$5e8960a0$@net>
Content-Type: text/plain; charset="us-ascii"

Hi There,
I'm new to the user group and pretty new to Linux too although I've been
using it blindly for about 10 years ! I've just built myself a mail server
on Ubuntu 14.04 using Postfix and Courier and whilst it seems to be working
well, I have started worrying about data security.

To this end I am planning to re-build it with a Raid setup. A lot of
googling has lead me to consider using Linux raid via mdadm (rather than the
'so-called' hardware BIOS raid built into my HP Proliant ML110 G5 server)
Ideally I would like the ability to hot swap drives. My questions centre
around - what raid solution should I choose and should I use a separate boot
disk ? I wondered if there was some helpful soul in the local Linux
community who would spare the time to educate me


Huw Morgan

-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2015.0.5645 / Virus Database: 4299/9231 - Release Date: 03/05/15




------------------------------

Message: 2
Date: Thu, 5 Mar 2015 16:43:47 -0000
From: "Martin Moore" <martinm@it-helps.co.uk>
To: <huw@cleevemill.net>, "'Bristol and Bath Linux User Group'"
<bristol@mailman.lug.org.uk>
Subject: Re: [bristol] Linux Raid
Message-ID:
<!&!AAAAAAAAAAAYAAAAAAAAAFLxZtQqo65Oo+1jhlUB9DvCgAAAEAAAAHOknUD1RnNNuN0UHHBssTsBAAAAAA==@it-helps.co.uk>

Content-Type: text/plain; charset="us-ascii"

mdadm works fine for me - but be aware you'll need to re-partition your
disks (they need to be Linux raid type) to use it so will lose everything.


Martin.

-----Original Message-----
From: bristol-bounces@mailman.lug.org.uk
[mailto:bristol-bounces@mailman.lug.org.uk] On Behalf Of Huw Morgan
Sent: 05 March 2015 16:24
To: bristol@mailman.lug.org.uk
Subject: [bristol] Linux Raid

Hi There,
I'm new to the user group and pretty new to Linux too although I've been
using it blindly for about 10 years ! I've just built myself a mail server
on Ubuntu 14.04 using Postfix and Courier and whilst it seems to be working
well, I have started worrying about data security.

To this end I am planning to re-build it with a Raid setup. A lot of
googling has lead me to consider using Linux raid via mdadm (rather than the
'so-called' hardware BIOS raid built into my HP Proliant ML110 G5 server)
Ideally I would like the ability to hot swap drives. My questions centre
around - what raid solution should I choose and should I use a separate boot
disk ? I wondered if there was some helpful soul in the local Linux
community who would spare the time to educate me


Huw Morgan

-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2015.0.5645 / Virus Database: 4299/9231 - Release Date: 03/05/15


_______________________________________________
Bristol mailing list
Bristol@mailman.lug.org.uk
https://mailman.lug.org.uk/mailman/listinfo/bristol
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2015.0.5751 / Virus Database: 4299/9226 - Release Date: 03/04/15




------------------------------

Message: 3
Date: Thu, 5 Mar 2015 20:18:14 +0000
From: Keith Edmunds <kae@midnighthax.com>
To: bristol@mailman.lug.org.uk
Cc: huw@cleevemill.net
Subject: Re: [bristol] Linux Raid
Message-ID: <20150305201814.42677c4a@ws.the.cage>
Content-Type: text/plain; charset=US-ASCII

Hi Huw

mdadm is the way to go: it simply works. If you've not used it before, I'd
suggest letting your installer set it up (most distros' installers will do
that for you). You don't need a separate boot disk, or even boot
partition. There are some clever things you can do, such as mirroring the
whole disk and layering LVM on top, but stick with what your installer
does.
--
"Soccer is one of those things that the rest of world cares about more
than [Americans] do - you know, like healthcare, education and gun
control" - David Letterman




------------------------------

Message: 4
Date: Thu, 5 Mar 2015 22:15:25 +0000 (GMT)
From: Alex Butcher <lug@assursys.co.uk>
To: huw@cleevemill.net
Cc: Bristol and Bath Linux User Group <bristol@mailman.lug.org.uk>
Subject: Re: [bristol] Linux Raid
Message-ID:
<alpine.LRH.2.11.1503052214360.31880@zlgugi.of5.nffheflf.cev>
Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII

On Thu, 5 Mar 2015, Huw Morgan wrote:

> I'm new to the user group and pretty new to Linux too although I've been
> using it blindly for about 10 years ! I've just built myself a mail server
> on Ubuntu 14.04 using Postfix and Courier and whilst it seems to be working
> well, I have started worrying about data security.
>
> To this end I am planning to re-build it with a Raid setup.

Good idea.

But remember that RAID isn't a substitute for backups. Moving on...

> A lot of googling has lead me to consider using Linux raid via mdadm
> (rather than the 'so-called' hardware BIOS raid built into my HP Proliant
> ML110 G5 server).

Actually, assuming the HP RAID implemention is like Intel's Rapid Storage
Technology (aka Matrix RAID aka fakeraid), there shouldn't be much
difference. Essentially, all these fakeraid solutions consist of are a)
BIOS kludges to allow booting from RAID volumes (and use of DOS, I suppose!)
and b) drivers which implement RAID, even if the OS doesn't (this is
particularly relevant for Windows where certain RAID levels are only
available in 'Enterprise' versions).

The most significant advantage of Linux md software RAID is that if the host
machine fails, you can remove the discs to another Linux machine and
assemble the array (assuming the kernel has md RAID support compiled in!)
regardless what make/model of controller(s) they're plugged into.

Proper hardware RAID has the advantage of providing tried-and-tested hotswap
and battery/flash/super-capacitor backed cache for enhanced performance and
data integrity. Very spendy!

> Ideally I would like the ability to hot swap drives.

If your BIOS is configured to present SATA drives as AHCI, you /should/ be
able to hotswap. In practice, I'd avoid it - too many untested combinations
could lead to surprises!

If you're insistent on hotswap, you'll probably also want hotswap caddies to
avoid knocking/dislodging/damaging other drives. Something like:

<http://www.startech.com/HDD/Mobile-Racks/Hot-Swap-SATA-SAS-Backplane-RAID-Bays-3-Hard-Drive-Mobile-Rack~SATSASBAY3BK>
<http://www.amazon.co.uk/s/ref=sr_nr_n_0?fst=as%3Aoff&rh=n%3A340831031%2Cn%3A430435031%2Ck%3Amb996&keywords=mb996&ie=UTF8&qid=1425573816&rnid=340832031>

Spendy!

> My questions centre around - what raid solution should I choose

I've been using Linux md RAID at home for over a decade. It's pretty good
these days.

I've recently set up an Intel RST array, and it seems broadly equivalent,
but some of the details of its operation (e.g. how it handles a read error
on one device in an array) when using the Windows drivers are opaque.

These days, I use and recommend Western Digital Red NAS drives for mirror
and parity RAID arrays (see the Features->NASware tab of
<http://www.wdc.com/en/products/products.aspx?id=810&utm_source=WD%20Red%20redirect&utm_medium=collateral&utm_content=en&utm_campaign=product#Tab2&Tab9>
for why - in brief, TLER and command completion). Note that the features of
such drives work against you in single drive or stripe RAID arrays, so don't
do that.

I always use hardware RAID with Western Digital RAID Edition drives in
professional settings.

> and should I use a separate boot disk ?

No need, really, providing you're booting from RAID 1 or RAID 10.

> I wondered if there was some helpful soul in the local Linux community
> who would spare the time to educate me

<http://linux.die.net/man/4/md> worth reading, also
<https://wiki.archlinux.org/index.php/RAID>

> Huw Morgan

HTH,
Alex



------------------------------

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