Alexander Graf wrote: > Anthony Liguori wrote: > >> On 05/17/2010 08:17 AM, Alexander Graf wrote: >> >>> On 17.05.2010, at 15:09, Anthony Liguori wrote: >>> >>> >>> >>>> On 05/17/2010 08:02 AM, Alexander Graf wrote: >>>> >>>> >>>>>> My concern is that ext3 exaggerates the cost of fsync() which will >>>>>> result in diminishing value over time for this feature as people >>>>>> move to ext4/btrfs. >>>>>> >>>>>> >>>>>> >>>>> There will be ext3 file systems for years out. Just because people >>>>> can use better and faster file systems doesn't mean they do. And >>>>> I'm sure they can't always choose. If anything, I can try and see >>>>> what the numbers look like for xfs. >>>>> >>>>> >>>>> >>>> But ext3 with barrier=1 is pretty uncommon in practice. Another >>>> data point would be an ext3 host file system with barrier=0. >>>> >>>> >>> Who defines what is common and what not? To me, the SLES11 default is >>> common. In fact, the numbers in the referred mail were done on an >>> 11.1 system. >>> >>> >> But it wasn't the SLES10 default so there's a smaller window of >> systems that are going to be configured this way. But this is >> orthogonal to the main point. Let's quantify how important this >> detail is before we discuss the affected user base. >> > > Alright. I took my Netbook (2GB of RAM) and a USB hard disk, so I can > easily remount the data fs the vmdk image is on. Here are the results: > > # mkfs.ext3 /dev/sdc1 > # mount /dev/sdc1 /mnt -obarrier=1 > > cache=writeback > > real 0m52.801s > user 0m16.065s > sys 0m6.688s > > cache=volatile > > real 0m47.876s > user 0m15.921s > sys 0m6.548s > > # mount /dev/sdc1 /mnt -obarrier=0 > > cache=writeback > > real 0m53.588s > user 0m15.901s > sys 0m6.576s > > cache=volatile > > real 0m48.715s > user 0m16.581s > sys 0m5.856s > > I don't see a difference between the results. Apparently the barrier > option doesn't change a thing. >
The same test case for XFS: cache=writeback real 0m50.868s user 0m11.133s sys 0m12.733s cache=volatile real 0m43.680s user 0m16.089s sys 0m7.812s Though I did have numbers here going as far down as 25 seconds for a run! Alex
