[clue] Greyhole

[Chris Fedde]

Raid 1 and raid10 are your only real choices when you have less than say 10
drives.  Raid 5 is considered unsafe for drives beyond 1T each because the
probability and consequence of a second drive failure during recovery.  You
need at least dual parity (Raid6).  Spares make the window to recovery a
little better but still your monitoring has to be reliable so that you
notice first drive failure before second drive failure.  At raid6 you have
a two drive penalty and with a spare it is a total of 3 drives overhead.

Here is a tool that covers most of the planning part:
https://www.icc-usa.com/raid-calculator

Of course raid does not protect you from the fat finger failure.  The raid
sub system will accurately and quickly remove the wrong thing any time I
ask it to.  For that reason on home systems I tend to go for two separate
file systems and a simple cron based copy from one to the other.  At least
then I can get back to yesterday's state easily enough.

BTW have you looked over the Drobo products? http://www.drobo.com/


On Mon, Jan 6, 2014 at 5:42 PM, <dennisjperkins at comcast.net> wrote:

>
> I talked with a couple of people today and we couldn't figure out how it
> might be better than RAID/LVM.  Maybe that's why MS dropped it from WHS?
>
> One guy has WHS and he doesn't use storage pools but he did configure it
> for RAID.
> ------------------------------
> *From: *"Quentin Hartman" <qhartman at gmail.com>
> *To: *"CLUE's mailing list" <clue at cluedenver.org>
> *Sent: *Monday, January 6, 2014 1:30:56 PM
> *Subject: *Re: [clue] Greyhole
>
>
> I've looked at it a couple times, but never actually used it. It managed
> to land in my "weird hack" pile, and so I never dove into it since more
> low-level things like RAID and LVM seemed to be better solutions. I'd be
> interested in hearing your thoughts after messing with it a bit though if
> you do. Particularly if you can come up with a use case where it's clearly
> better than RAID/LVM. The only thing I could come up with is if could
> spread data across multiple machines, but that doesn't seem to be supported.
>
> And yes, WHS has/had storage pools like that, but it is more low level
> than how greyhole seems to work. It seems to do something just above the FS
> layer to create redundant copies of files on the participant disks, so it's
> effectively similar to greyhole, but doesn't have the propagation delay
> that greyhole does if a disk disappears, but it's not really RAID either. I
> only messed with this briefly before nuking the WHS install on my box and
> replacing it with a *nix, so apply salt.
>
> Q
>
>
>
>
> On Mon, Jan 6, 2014 at 12:52 PM, <dennisjperkins at comcast.net> wrote:
>
>> Has anyone heard of or used Greyhole?  Amahi and Openmediavault have it.
>> It uses Samba to create a storage pool of disks. Apparently Windows Home
>> Server used to have a storage pool too.
>>
>> I'm not sure what advantage it has over RAID, unless the ability to have
>> more than two copies is important..  You can configure it to make 1 or more
>> copies of files that have been copied into landing zones (shares).  The
>> files are copied onto one or more drives, depending on the configuration
>> settings, and the original files in the landing zones are replaced with
>> links.  If a drive crashes, you can still get to the files on other drives.
>>
>> MySQL is also used.  That seems overly complicated but I don't know
>> enough about how Greyhole works to know why it's needed.  Maybe transaction
>> logs?  Maybe that's how it deals with files that have been deleted, moved
>> or renamed.
>>
>> It also seems odd that it uses Samba.  Why not make it lower level?  Then
>> Samba or NFS could use it.
>>
>> I have not tried it.  Maybe I'll do so with OMV.
>>
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