Hi all, like Tyler I'm also asking me those questions. Reason is that newer Solid-State Drives (like the Intel 320 Series) have Flash-Chips with page size of 8KiB (the former SSDs have mostly 4KiB pages). So in the best case, all data written to such an SSD should be at least 8KiB aligned - which I think is not the case for MD-RAID with metadata 1.2 superblocks - because of the "4K from the beginning of the device": https://raid.wiki.kernel.org/index.php/RAID_superblock_formats#Sub-versions_of_the_version-1_superblock When I understand the wiki page correctly, the metadata 1.2 superblock has a size of 1024 Bytes (256 Bytes + 2 Bytes/device for a maximum of 384 devices), right? When I simply put an Ext4 file system with a block size of 4KiB on the RAID, there is no problem as there will always be two Ext4 blocks residing in a single 8 KiB page of the SSD. My questions: 1) But when I use LVM2 with a PE size of 4 MiB on top of a RAID, I will not be perfectly aligned any more, right? 2) Are there any plans that e.g. the first 1MiB will be reserved for metadata (like fdisk does when creating new partitions), so that there won't be any alignment issues in the future? (btw: haven the metadata at the end of the device like in the metadata format 0.90 or 1.0 would also not interfere the alignment - is there a special reason why the metadata has been put to the beginning of the device?) best regards, Werner On Wed, 2011-07-06 at 08:11 +0100, Tyler J. Wagner wrote: > Hi all (well, Neil, really), > > The the following, Neil states that that is no issue with alignment of > metadata 1.2 and mkfs.ext4 on 4K drives: > > http://www.issociate.de/board/post/507176/filesystem_on_mdadm_raid_from_unpartioned_block_devices.html > > Sorry to ask again, but I just want to clarify. Metadata 1.2 puts the > data 4K from the start of the device/partition. Does mkfs put the start > of the filesystem at 64K from the start? IE, will the following align, > without any need for options? > > (create partitions starting 2048 512-byte sectors from start = 1MB) > mdadm --create /dev/md0 -v --raid-devices=4 --level=raid10 > --metadata=1.2 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1 > mkfs.ext4 /dev/md0 > > And, slightly off-topic, it's not necessary to define stride and stripe > any longer? > mkfs.ext4 -E stride=16,stripe-width=32 /dev/md0 > > Regards, > Tyler > > -- : Werner Fischer : Technology Specialist : Thomas-Krenn.AG | The server-experts : http://www.thomas-krenn.com | http://www.thomas-krenn.com/wiki -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
