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

Timo Schoeler timo.schoeler at riscworks.net
Thu Dec 10 09:28:40 UTC 2009


[off list]

>>>> Thanks for your eMail, Ross. So, reading all the stuff here I'm really 
>>>> concerned about moving all our data to such a system. The reason we're 
>>>> moving is mainly, but not only the longisch fsck UFS (FreeBSD) needs 
>>>> after a crash. XFS seemed to me to fit perfectly as I never had issues 
>>>> with fsck here. However, this discussion seems to change my mindset. So, 
>>>> what would be an alternative (if possible not using hardware RAID 
>>>> controllers, as already mentioned)? ext3 is not, here we have long fsck 
>>>> runs, too. Even ext4 seems not too good in this area...
>>> I thought 3ware would have been good. Their cards have been praised for 
>>> quite some time...have things changed? What about Adaptec?
>> Well, for me the recommended LSI is okay as it's my favorite vendor, 
>> too. I used to abandon Adaptec quite a while ago and my optinion was 
>> confirmed when the OpenBSD vs. Adaptec discussion came up. However, the 
>> question on the hardware RAID's vendor is totally independent from the 
>> file system discussion.
> 
> Oh yeah it is. If you use hardware raid, you do not need barriers and 
> can afford to turn it off for better performance or use LVM for that matter.

Hi, this ist off list: Could you please explain me the LVM vs. barrier 
thing?

AFAIU, one should turn off write caches on HDs (in any case), and -- if 
there's a BBU backed up RAID controller -- use this cache, but turn off 
barriers. When does LVM come into play here? Thanks in advance! :)

>> I re-read XFS's FAQ on this issues, seems to me that we have to set up 
>> two machines in the lab, one purely software RAID driven, and one with a 
>> JBOD configured hardware RAID controller, and then benchmark and stress 
>> testing the setup.
> 
> JBOD? You plan to use software raid with that? Why?!

Mainly due to better manageability and monitoring. Honestly, all the 
proprietary tools are not the best.

Timo


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