[clue] Greyhole

[Dennis J Perkins]

Do you like the idea of storage pools?  Do you think they are a good idea?

I hadn't looked at Drobo until you and Sean mentioned it.  Not cheap but one of the 5-bay systems is a little less than I spent.  Apparently they have a proprietary drive format.  Maybe Synology would be better.

On Jan 6, 2014 6:51 PM, Chris Fedde <chris at fedde.us> wrote:
>
> 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.
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> BTW have you looked over the Drobo products? http://www.drobo.com/
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> On Mon, Jan 6, 2014 at 5:42 PM, <dennisjperkins at comcast.net> wrote:
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>> 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.
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>> Q
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>> On Mon, Jan 6, 2014 at 12:52 PM, <dennisjperkins at comcast.net> wrote:
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>>> 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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>>
>>
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