On Monday, 24 June 2019 18:00:29 BST Peter Humphrey wrote: > On Monday, 24 June 2019 16:59:08 BST Grant Taylor wrote:
> > > On this box, which does need lvm for RAID-1 on two SSDs: > > Do you /need/ LVM? Or is it extra that comes with device-mapper? > > No, I do actually use lvm to base a raid-1 file system on. I haven't > considered raid-1 without lvm; is that feasible? Almost totally. They two are separate functions with synergistic interaction. RAID 1 offers redundancy by mirroring data between two block devices. LVM offers a flexible partitioning scheme where you can add space, move, snapshot, etc. data using a logical software layer to manage their storage across partitions and physical disks. I've put together RAID 1 disks with no LVM and used LVM with no RAID. NOTE: To confuse things you can instead use LVM's built in 'RAID functionality' - see below. I recall reading somewhere that SSDs are better used with LVM's natively configured RAID functionality, rather than a separate RAID layer, which in a mirrored RAID it will cause accelerated wear due to the way RAID metadata are mirrored between block devices. I don't think I've ever used LVM's RAID capability, but it would probably boil down to running: lvcreate --mirrors 1 --type raid 1 -n LV_myRAID VG_blah-blah Others more knowledgeable in these technologies could chime in to correct me no doubt. PS. LVM-RAID uses the kernel's mdraid, but with less tools to manage the RAID configuration than mdadm offers: https://unix.stackexchange.com/questions/150644/raiding-with-lvm-vs-mdraid-pros-and-cons -- Regards, Mick
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