[CentOS] XFS and LVM2 (possibly in the scenario of snapshots)

Timo Schoeler timo.schoeler at riscworks.net
Wed Dec 9 15:39:53 UTC 2009


thus Ross Walker spake:
> On Dec 9, 2009, at 8:05 AM, Timo Schoeler  
> <timo.schoeler at riscworks.net> wrote:
> 
>> Hi list,
>>
>> during the last days there was a discussion going on about the  
>> stability
>> of XFS; though I myself used XFS heavily and didn't run into issues  
>> yet,
>> I'd like to ask something *before* we create our next generation data
>> storage backend...
>>
>> Les Mikesell wrote in [0] about issues in the combination of XFS and  
>> LVM
>> -- however, it was being discussed in context of using 32bit kernels.
>>
>> What I specifically need is to run XFS (or something similar, I am  
>> *not*
>> forced to use XFS, but it was my preference for some years now, and I
>> didn't have any issues with it yet) on top of LVM to be able to create
>> snapshots. We're talking about several file systems of a size at about
>> 4TiByte each.
>>
>> On another place [1] I read that there were issues with that.
>>
>> Can anyone shed some light on this? Would be very appreciated.
> 
> There is no problem if it is done on x86_64 with it's 8k stack frames,  
> but on i386 with it's 4k stack frames you could run into a stack  
> overflow when doing it on top of stackable block devices (md raid,  
> lvm, drbd, etc).
> 
> Also since the current LVM on CentOS doesn't support barriers (next  
> release I believe) journalling isn't safe on LVM unless you are using  
> a storage controller with BBU write-back cache.
> 
> I have heard anyways that the current implementation of barriers isn't  
> very performant and doesn't take into consideration controllers with  
> BBU cache, so most people will end up mounting with nobarriers which  
> just means they are in the same boat as they are now. Better make sure  
> your machine is bullet proof as a power outage or a kernel panic can  
> spell disaster for XFS (or any other file system really).
> 
> It is better to invest in a good hardware RAID controller until the  
> whole barriers stuff is ironed out. It should really perform better  
> then it does.

Thanks for your detailed explanation, that really clears things up; 
however, I was intending to build a software RAID10 as we had really not 
so good experiences on hw RAID controllers int the past (for all kinds 
of phenomena).

Would barriering here still be a problem then?

Timo

> -Ross



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