Re: Mixing HDD and SSD in lvm

[Dan Ritter <dsr@randomstring.org>]

Kamil Jońca wrote: 
> 
> Debian box with LVM
> LVM uses  2 PV - raid devices each uses 2 HDD (rotating)
> discs (with sata interfaces).
> 
> Now I am considering replacing one PV with md device constisting of SSD
> discs, so LVM will be have one "HDD" based pv and one SSD based PV.
> Should I worry about anything (speed differences or sth)?

1. Refer to the disks in mdadm with the /dev/disk/by-id names, not
/dev/sdb style names.

2. Use mdadm's RAID-1 with the write-intent bitmap feature and
specify that the spinning disk will use the write-mostly
feature.

RAID 0 will be bad; don't try it.

Good luck; I've never actually tried this, but thought about
quite a bit.

-dsr-