On Mon, 2011-07-25 at 13:23 -0400, R P Herrold wrote: > On Mon, 25 Jul 2011, Les Mikesell wrote: > > > My questions for any filesystem experts are: > > > > Is there a way to adjust the existing md partitions to get the right > > alignment for 4k sectors without having to do a file-oriented copy to > > new partitions? A resize + a dd copy to shift the position might be > > feasible time-wise if that would work. > > no expert here, but I have the scars across my back from > pulling arrows out, as a pioneer > > We have hit the issue on our storage backend which runs ext4, > and on some of our dom0 built before the 4k sector alignment > was generally acknowledged and known to be potentially in play > > We have some non-conformant units, and after seaching, > concluded that a 'wipe and rebuild' was the most time > efficient process for us -- YMMV > > > Is it worth converting to ext4? > > ext4 is pleasant in some large filesystem cases, but probably > overkill as a blanket option. > > Certainly it is 'wayy overkill for domU as a general rule, as > it makes for a more fragile image in the sense that generic > tools are less likely to work without higher version and skill > levels when a filesystem gets horked up and a repair > expedition has to be mounted ... we had an issue that a > 'dirty' filesystem that would not fsck kept showing up in a > nightly backup exception report, and ended up manually > repairing what should have been able to be repaired > automatically > > > Is there a difference between doing this on 5.6 or 6.x? > > in C5, it took extra effort to use the technology preview; in > C6 it is natively available > > > If I start over from scratch with 6.x, will the partitioning tools > > automatically align for 4k sector drives (with/without lvm?)? > > no idea if gparted does this by default -- it does not in all > versions; certainly fdisk did not -- 4k alignment is on our > deployment checklist, and we are manually checking > partitioning to make sure, when we are rebuilding boxes > I can only comment on the last section I have built Centos 6.0 on a SSD using F15 version of gdisk man gdisk shows for the l option "Change the sector alignment value. Disks with more logical sectors per physical sectors (such as some Western Digital models introduced in December of 2009) and some RAID configurations can suffer performance problems if partitions are not aligned properly for their internal data structures. On new disks, GPT fdisk attempts to align partitions on 2048-sector (1MiB) boundaries by default, which optimizes performance for both of these disk types." Only straight ext4 parttions (No lvm) I have seen no problems so far ... Number Start (sector) End (sector) Size Code Name 1 2048 4095 1024.0 KiB EF02 BIOS boot partition 2 4096 2101247 1024.0 MiB 0700 Linux/Windows data 3 2101248 6295551 2.0 GiB 8200 Linux swap 4 6295552 69210111 30.0 GiB 0700 Linux/Windows data 5 69210112 132124671 30.0 GiB 0700 Linux/Windows data 6 132124672 174067711 20.0 GiB 0700 Linux/Windows data 7 174067712 468862094 140.6 GiB 0700 Linux/Windows data John