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I've read that SSD TRIM is now supported in the recent kernels with ext4 too (see How to enable TRIM? ).

Is it OK/safe to enable TRIM when having a) LVM b) RAID1+LVM?

Thanks!

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Device Mapper based RAID e.g. via dmsetup does support TRIM MD raid e.g. via mdadm does not support TRIM.

http://www.redhat.com/archives/linux-lvm/2010-October/msg00066.html

This might have changed, but a quick grep of the oneiric kernel (git grep REQ_DISCARD drivers/md)doesn't show any specific support in the MD code for discards. It might be worth searching the MD RAID mailing list to see how this has progressed.

Speaking from experience, I am not a big fan of using DM for managing RAID sets, the tools are kinda cumbersome and basic admin tasks are a burden; and so is recovering a failed RAID. If you want to take the plunge I strongly recommend you model the setup in a VM so you can become accustomed with the toolset's ins and outs. BTW, don't get confused by dmraid, that's for fake raid only.

http://mbroz.fedorapeople.org/talks/DeviceMapperBasics/dm.pdf

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