[ML-General] hardware RAID

[Kirk D Mccann]

So I've noticed two things that no one has mentioned yet.  3 drives running
in raid 0 and rebuild times of large drives.

Raid 0:
You realize that if any one of the drives that are running in raid 0 fail
then you lose all your data right?  The only time you want to use raid 0 is
when you dont care about the data and are looking for speed.  I use raid 0
for our build server build drive because we always have source code that
can be used to rebuild the builds.

Large Drives:
So if you have more two drives mirroring isnt really what you want because
true mirroring only works with two sets.  (That could be two drives or two
sets of raided disks).
Since you have more than two drives you are going to want raid 5,6, or 7.
The raid that you choose should be based on the size of your drives and the
class of the drives.

If the drives you have are more than 1TB in size and they are consumer
grade drives then you shouldn't be using raid 5.
This is a problem because the likelihood of a read failure while rebuilding
a disk is higher the larger the drives are.  So then you have to be able to
handle a read failure which requires a higher raid.  Check out the
calculator:
http://www.servethehome.com/raid-calculator/raid-reliability-calculator-simple-mttdl-model/

Also if you are using raid dont use Western Digital Green drives unless you
plan to reflash the firmware to make them function like red drives.

My recommendation:
All that being said I am a big fan of Freenas, because it uses ZFS.  Btrfs
is great but its not quite where ZFS is yet(or at least that was the case
when I last looked at it).  If you go the ZFS route you REALLY REALLY need
to read up on how ZFS, uDevs, and vDevs work.  Because what many people
dont realize is you cant just add a single disk to the array when you do it
makes the entire array fail if that single added disk fails.  When you add
drives you have to add drives in sets.

Personally I'm paranoid about my data, I use ZFS raid z3 on two vDevs, each
vDev has 5 2+TB drives.

Oh and with ZFS you can use different size drives but you waist a good
amount of space when you do that.
And lastly be sure to schedule scrubs of your drives and do it in a way
that the scrub will not occur while a long smart test is running.  That can
cause problems.

-Kirk

On Thu, Jun 11, 2015 at 5:33 PM, WebDawg <webdawg at gmail.com> wrote:

>
>
> On Thu, Jun 11, 2015 at 3:30 PM, WebDawg <webdawg at gmail.com> wrote:
>
>> On Thu, Jun 11, 2015 at 3:11 PM, david <ainut at knology.net> wrote:
>>
>>>  I'm thinking about putting all the computers on the network disk array,
>>> including the SOC's: beaglebone blacks, arduino mega256, and the RPi2.  I
>>> would not mind doing the compiles (and maybe even the booting!) on the hard
>>> drives instead of the limited-life SD cards and 'flash' that are on the
>>> SOC's.  Any of you guys done that?  Everything in the house is 1Gb
>>> Ethernet.  If only I could get that to the outside world <heavy sigh.>  :-)
>>>
>>>  Already have the BBB's booting of the SD card, which you have to do
>>> with the rev B's and their 2 Gb size..
>>>
>>> David
>>>
>>>
>> I have thought about it.  At that point you need to consider the
>> transport mechanism between the systems and such. NFS, CIFS, iSCSI?
>>
>> You need to back up.  Live. (ZFS Snapshot)
>>
>> I do not know what you do with them, so I cannot help there.
>>
>> PXE boot?  Other ways to boot?  I do not know a lot about that stuff
>> except the RPi.
>>
>> I would consider bonding more then one port together on the network
>> server if you are doing anything major.
>>
>> I run some VMS over NFS right now, I do not like it.
>>
>> I was using CIFS but after learning that is really bad to do over and
>> over again.  I stopped.  None of this was mission critical.
>>
>> I want speed so I am leaning towards some physical disks for the virtual
>> systems.  In the future I would use a fiber target or bonded target that
>> was dedicated if I wanted network stuff.
>>
>> Fun Fun.
>>
>
> I forgot to mention.  You are going to need a few UPS units.  I have
> destroyed virtual systems when a server that hosts its filesystem has went
> down.  It is not fun bringing it back to life.
>
> If you are talking about creating and image, and having the devices pull
> any new images when new ones exist, still using them on the SD cards while
> they are on, I think you have a different situation all together.
>
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