Am 27.04.2017 um 21:03 schrieb John Stoffel:
Mateusz> They will be synced one by one, just like one big md device. No, big MD devices are sync'd in parallel assuming MD thinks they're on seperate devices
if they are on sepearte drives it's no problem and no "seek storm"
Now in this case I admit I might have jumped the gun, but I'm mostly commenting on the use of multiple MD RAID setups on a single pair of disks. It's inefficient. It's a pain to manage. You lose flexibility to resize.
which don't matter if you have LVM on top
Just create a single MD device across the entire disk (or possibly two if you want to boot off one mirrored pair) and then use LVM on top to carve out storage. More flexible
but you can't boot from a RAID5/RAID6/RAID10 so you have a single point of failure of a single boot disk or need at least two additional disks for a redundant boot device
frankly on a proper designed storage machine you have no need for flexibility and resize because for it's entire lifetime you have enough storage at all and in case of LVM it don't matter how many md-devices are underlying the LVM
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