On Aug 24, 2014, at 11:08 AM, Jarkko Oranen wrote: > Hello > > Yesterday I experimented a bit with my RAID configuration on a pair of > SSDs, and it seems that LVM's native RAID does not have TRIM support... > At least, when I try to run fstrim manually, it complains even though > issue_discards is enabled. Plain LVs on top of an MD RAID PV do work, of > course. > > Am I perhaps missing some configuration, or do RAID1 logical volumes > simply not have support for TRIM yet? I'm running a fairly recent kernel > (3.15.8) and lvm version says this: > > LVM version: 2.02.106(2) (2014-04-10) > Library version: 1.02.85 (2014-04-10) > Driver version: 4.27.0 TRIM is not yet supported in LVM RAID. However, if MD has a solid TRIM implementation, it should be simple to enable it for LVM. (This is because the MD kernel modules are used to perform RAID for LVM. There is only a thin wrapper layer (linux/drivers/md/dm-raid.c) in device-mapper used to set-up the device.) > As an aside, can anyone point me to documentation or other resources > about the pros and cons of LVM native RAID1 setup (which I understand > uses MD RAID internally?) vs. MD RAID PV + LVM. It seems I might be able > to save some SSD space and only mirror the LVs I actually need to keep > safe from crashes. I don't know if there is a specific list to point to out there, but I can give you a couple pros/cons. PRO: - use one volume manager instead of two - LVM is better suited to creating devices of varying sizes - leaving spare capacity for snapshots, etc CONS: - no trim support with RAID through LVM (although, I'm not sure of the state in MD) - no reshaping (changing from one RAID type to another) capability in LVM RAID. brassow _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
