[CentOS] Is ext4 safe for a production server?

Ross Walker rswwalker at gmail.com
Sun Dec 13 22:08:13 UTC 2009


On Dec 13, 2009, at 10:15 AM, Pasi Kärkkäinen <pasik at iki.fi> wrote:

> On Fri, Dec 11, 2009 at 09:20:24AM +0800, Christopher Chan wrote:
>> Mark Caudill wrote:
>>> Christopher Chan wrote:
>>>> Morten Torstensen wrote:
>>>>> On 08.12.2009 13:34, Chan Chung Hang Christopher wrote:
>>>>>>> Speaking for me (on Linux systems) on top of LVM on top of md.  
>>>>>>> On IRIX
>>>>>>> as it was intended.
>>>>>>>
>>>>>> That is a disaster combination for XFS even now. You mentioned  
>>>>>> some
>>>>>> pretty hefty hardware in your other post...
>>>>> If XFS doesn't play well with LVM, how can it even be an option? I
>>>>> couldn't live without LVM...
>>>>>
>>>> I meant it in the sense of data guarantee. XFS has a major  
>>>> history of
>>>> losing data unless used with hardware raid cards that have a bbu  
>>>> cache.
>>>> That changed when XFS got barrier support.
>>>>
>>>> However, anything on LVM be it ext3, ext4 or XFS that has barrier
>>>> support will not be able to use barriers because device-mapper  
>>>> does not
>>>> support barriers and therefore, if you use LVM, it better be on a
>>>> hardware raid array where the card has bbu cache.
>>>
>>> Wait, just to be clear, are you saying that all use of LVM is a  
>>> bad idea
>>> unless on hardware RAID? That's bad it if it's true since it seems  
>>> to me
>>> that most modern distros like to use LVM by default. Am I missing  
>>> something?
>>>
>>
>> Yes, the Linux kernel has long been criticized for a fake
>> fsync/fsyncdata implementation. At the latest, since 2001. Unless you
>> had your hard drive caches turned off, you were at risk of losing  
>> data
>> no matter what you used: ext2, ext3, reiserfs, xfs, jfs, whether on  
>> lvm
>> or not.
>>
>> Write barriers were introduced to give data guarantees with hard  
>> drives
>> that have their write cache enabled. Unfortunately, not everything  
>> has
>> been given barrier support. LVM and JFS do not have write barrier  
>> support.
>>
>
> https://www.redhat.com/archives/dm-devel/2009-December/msg00079.html
>
> "Barriers are now supported by all the types of dm devices."

I wonder how long till it's backported to RHEL?

-Ross



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