On 09/13/2012 09:00 PM, Josef Bacik wrote: > On Thu, Sep 13, 2012 at 12:02:04AM -0600, ching lu wrote: >> I am trying to test btrfs on my ssd, i am studying about btrfs and alignment. >> >> I have read this old mail: >> http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg16177.html >> >> According to the thread, 3 parameters should be tuned >> >> 1. leafsize >> 2. nodesize >> 3. sectorsize >> >> The first two parameters are easy to understand, but how does >> "sectorsize" affect the alignment? >> >> If the erase block size of my SSD is 16k, and i set >> leafsize=nodesize=16k, leave the sectorsize=4k (default), will it >> causes misalignment? > So frist leafsize/nodesize will always be the same, so if you set one to 16k > mkfs will autmatically set the other to 16k, it's just way back when we had > grand plans of having different sizes for both. > > Secondly your erase block size is 16k? What kind of drive are you using? But > yeah 4k sectorsize will result in misaligned writes to the data area, but your > metadata will be aligned. Hopefully the raid5/6 code will be out soon and > we'll > be able to do > page size sectorsize and you'll be able to set > leafsize==sectorsize. Btw most normal SSDs have waaaay larger erase blocks, > on > the order of several MB, so it's not the worst thing to write to the middle of > erase blocks, everybody does it anyway. Thanks, > > Josef >
16k is just a assumption only, thanks for your help anyway. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
