Does BTRFS perform any journal and/or filesystem structure alignment (for benefit to SSD longevity and SSD, RAID array and large-sector device performance) at present? ext4''s Ted Tso will deliver 128KB alignment with the next release of e2fsprogs (ie 1.41.4) [1], so perhaps it''s a good idea for btrfsprogs also, if not already available? Daniel --- [1] http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/ -- Daniel J Blueman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, Feb 22, 2009 at 11:31 PM, Daniel J Blueman <daniel.blueman@gmail.com> wrote:> Does BTRFS perform any journal and/or filesystem structure alignment > (for benefit to SSD longevity and SSD, RAID array and large-sector > device performance) at present? > > ext4''s Ted Tso will deliver 128KB alignment with the next release of > e2fsprogs (ie 1.41.4) [1], so perhaps it''s a good idea for btrfsprogs > also, if not already available? > > Daniel > > --- > [1] http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/ >I think the partition alignment is more important because it has been traditionally hard-coded as 63 sectors. However, the misalignment by filesystem or *fsprogs are of block-sized granularity (usually 4KB). Ted mentioned that the Vista changed the default CHS to 240 heads and 62 sectors. However, AFAIK, what Vista does for that alignment is to change the relative sectors of the MBR [1] -- Dongjun [1] http://www.multibooters.co.uk/partitions.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, 2009-02-22 at 14:31 +0000, Daniel J Blueman wrote:> Does BTRFS perform any journal and/or filesystem structure alignment > (for benefit to SSD longevity and SSD, RAID array and large-sector > device performance) at present? > > ext4''s Ted Tso will deliver 128KB alignment with the next release of > e2fsprogs (ie 1.41.4) [1], so perhaps it''s a good idea for btrfsprogs > also, if not already available? >The btrfs metadata works a little differently from ext4, since almost nothing is in a fixed place. The super blocks are aligned to 64k, and the rest of the metadata is all dynamic. Today, metadata allocations are 4k aligned but we do metadata allocations in cluster of 256k in size (2MB in size in mount -o ssd mode). This results in larger metadata writes, and more contiguous metadata writes. The larger writes give the SSD FTL a better chance of doing more optimal management of the flash. Additional tuning for specific alignment is possible as well, the kernel is growing the ability to discover device alignment characteristics, and I plan on taking advantage of that. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html