[mdlug] New Server - Hardware Configuration

[Aaron Kulkis]

Robert Adkins II wrote:
> The plan is to copy all of the data to the hot swap drives and... 
> 
> Swap them out every day, every few days.


Bad idea.  Keep two set of drives permanently installed, set 2 fully mirroring set 1.
These can (and should) be hot-swappable, but none of these drives should be swapped
unless the unit in question fails.

a THIRD set of hardware addresses should be mapped to hot-swapable bays, and
by turning mirroring on and off, a snapshot of the filesystem state can be
obtained with no system downtime and only momentary application service downtime.

[I used to work in the financial sector, where this stuff is important -- good
backups are required by LAW, and this method works well, both reliably and efficiently.].

Doing round-robin rotation of your disks is a good way to have all of your
disks hit MTBF (mean-time-between-failure) in rapid succession -- which is
NOT a good thing.  You want disk failures to be staggered in time, not
cascading at you like an avalanche.

> 
> There would essentially be upwards of 6 full copies, two of which would be
> 100% current and 1 that might be 1 to 2 days behind, of everything on the
> server.
> 
> They aren't pushing the design, I called them and explained what I was
> looking to do.
> 
> I haven't really dug into SAN technology and I am wary of tying data into
> something that could leave me with an unproduceable (or very difficult to
> reproduce) system in the event of a motherboard hardware failure.
> 
> -Rob
>  
> 
>> -----Original Message-----
>> From: mdlug-bounces at mdlug.org 
>> [mailto:mdlug-bounces at mdlug.org] On Behalf Of Michael ORourke
>> Sent: Sunday, April 22, 2012 11:02 PM
>> To: MDLUG's Main discussion list
>> Subject: Re: [mdlug] New Server - Hardware Configuration
>>
>> What about a small SAN device?  Also, you could attach an 
>> iSCSI SAN to a front-end Linux server.  Another thing you 
>> didn't mention was backups. 
>> Having multiple RAID sets is NOT a backup strategy.  This is 
>> a common mistake many people make.
>> If it were me, I would try to seperate the storage from the 
>> server.  Perhaps with a RAID6 configuration and a hot spare.  
>> That way you could lose up to 3 drives and still be fully 
>> operational.  There are several low cost SAN vendors out 
>> there which are certainly worth a look.  I don't quite 
>> understand why they are pushing a server with 3 RAID cards.  
>> Sounds like this might become an expensive and difficult to 
>> support file server.
>>
>> -Mike
>>
>> ----- Original Message -----
>> From: "Robert Adkins II" <radkins at impelind.com>
>> To: "'MDLUG's Main discussion list'" <mdlug at mdlug.org>
>> Sent: Thursday, April 19, 2012 8:34 AM
>> Subject: [mdlug] New Server - Hardware Configuration
>>
>>
>>> It's time to upgrade the old servers here at the office.
>>>
>>> Here's the plan:
>>>
>>> Matched pair of HDs for the Main OS Drive. These will be mirrored.
>>>
>>> Matched Pair or two matched pairs of drives for 
>> Filesharing. These will be
>>> mirrored.
>>>
>>> Separate RAID Card that supports Hot Swap on Linux to allow 
>> for two to 
>>> three
>>> removable drive bays that will be used to duplicate the 
>> entirety of the
>>> mirrored data drives.
>>>
>>> I have a quote from Dell for a server that uses their Linux 
>> Compatible 
>>> RAID
>>> cards. Right now, they are quoting three RAID Cards. The 
>> onboad card that
>>> the OS will be booting off of, a second card that will be 
>> for the data
>>> drives and a final card that won't be setup as RAID, which 
>> means that it
>>> won't/shouldn't crap out the kernel while supporting hot swapping.
>>>
>>> Thoughts? Opinions?
>>>
>>> Thanks.
>>>
>>>