[OpenIndiana-discuss] Need thoughts on OpenIndiana+ZFS for backup server

[Matt Wilby]

On 05/02/2011 13:03, Gary Gendel wrote:
> I tend to agree with Matt.
>
> I've had several catastrophic power incidence on my server running
> OpenSolaris without incident (such as a UPS gone haywire).  Since ZFS
> does transaction-safe reads and writes, the consistency on the disk
> has an extremely low probability of getting corrupt. But there are
> always two things to consider...  Powering off the server this way
> could cause the disks themselves to write garbage and ZFS (or any
> other filesystem) won't have the opportunity to fix it.  Also, there
> may be pending things in the ZFS cache which won't be written.  You
> can disable the ZFS cache, but that will impact performance.
>
> If it's a situation where you don't have control over the servers
> (someone turns off the master switch), then I truly suggest that you
> put a UPS on the server and have a daemon (nut, apsupcd, etc.) that
> get's the signal that the power has been killed and shuts down the
> servers gracefully.
>
> Based upon the goals of Hammer, it looks like ZFS covers them all.  It
> looks like, on Hammer, you have to run a a prune/reblock on the
> filesystem nightly to conserve resources.  I would assume that heavily
> pounding during the day will limit the effective utilization greatly. 
> How much overhead do you need for the prune/reblock, 10%, 20%?  What
> happens if there isn't enough room to run it?
>
> You're skirting on very thin ice if you pull the plug to shut down the
> servers no matter what system you use.  Interestingly, there are no
> specs for Hammer in the FS comparison chart.  This doesn't sound like
> a seasoned production filesystem which would scare me even more.
>
> On 2/5/11 6:35 AM, Matt Wilby wrote:
>> On 05/02/2011 11:28, Basil Kurian wrote:
>>   
>>> Here we are running backup servers only during business hours (web
>>> development firm). At the end of day , Sometimes the servers are
>>> powered
>>> off  , without issuing any commands to shutdown them cleanly.
>>>
>>> On 5 February 2011 16:45, Matt Wilby<matthewwilby at btinternet.com> 
>>> wrote:
>>>
>>>     
>>>> On 05/02/2011 10:53, Basil Kurian wrote:
>>>>       
>>>>> Hi all
>>>>>
>>>>>
>>>>> Currently in our company we are having a Dragonfly BSD backup
>>>>> server with
>>>>> Hammer filesystem in it. One senior system administrator in our
>>>>> compay
>>>>>          
>>>> chose
>>>>       
>>>>> Hammer filesystem some times back, because Hammer filesystem can
>>>>> easily
>>>>> recover in times of power failures. I 'm compelling him to move to
>>>>> ZFS
>>>>>          
>>>> (on
>>>>       
>>>>> FreeBSD or OpenIndiana). How durable is data on an ZFS pool (RAID or
>>>>>          
>>>> mirror)
>>>>       
>>>>> when  power failure happen frequently.
>>>>>
>>>>>          
>>>> Hi,
>>>>
>>>> I use ZFS on my backup servers. I can't say we've ever had power
>>>> failures because they're in a datacenter, but I would invest in a
>>>> decent
>>>> UPS if it's a regular occurrence. Hard drives don't generally like
>>>> having power suddenly removed.....
>>>>
>>>> ZFS on OpenIndiana will give you nice features like file system
>>>> compression, dedupe, snapshots and constant checksumming of of in-use
>>>> blocks.
>>>>
>>>> I've never used Hammer before, but HammerFS doesn't appear to offer
>>>> compression yet.
>>>>
>>>> Just my opinion, but I'd say ZFS is more widely used than Hammer.
>>>>
>>>> Matt
>>>>
>>>>
>>>>
>>>> _______________________________________________
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>>>> OpenIndiana-discuss at openindiana.org
>>>> http://openindiana.org/mailman/listinfo/openindiana-discuss
>>>>
>>>>        
>>>
>>>      
>> I don't understand why you would ever want to shut a server down in this
>> way.
>>
>> Can't you just setup a cron to shut them down at a certain time?
>>
>>
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>>    
>
>
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One other thing to consider if you are going to use Hammer is that it
appears to require a cron job to be run to free up space/blocks in order
to recover space on the file system.

To quote the manual -

"The system cron automatically runs HAMMER cleanup functions at least
once a day."


So obviously make sure you move the cron job to run whenever the server
is up. Don't know how this impacts operational performance. I would feel
uneasy about relying on a cron job to perform essential file system tasks.