Scampicfx
Contributor
- Joined
- Jul 4, 2016
- Messages
- 125
Dear folks,
I'm still in preparation of building my first FreeNas system. While thinking of doing an all-SSD-based solution versus HDD-based-server following questions arised:
1.) - What happens when a zpool consists of multiple vdevs of different disk numbers and different disk sizes and even different RAID-levels?
2.) - What happens when a zpool consists of multiple vdevs, each vdev containing the same number of disks, however different disk sizes, same RAID-levels?
Example for 1.)
vdev A: 6x 6TB (RAID-Z2)
vdev B: 9x 1TB (RAID-Z3)
Example for 2.)
vdev A: 6x 2 TB (RAID-Z2)
vdev B: 6x 4 TB (RAID-Z2)
I'm especially interested in 2) because I'm thinking of starting a "small" FreeNas Server based on 6x 2 TB SSDs and add additional capacity by adding additional vdevs with bigger drives at a later point, when SSDs prices get cheaper.This would mean that I start with vdev A and add vdev B in maybe one or two years.
How is the striping-performance affected when each vdev is different in total capacity? How gets a file stored (e.g. 10 MByte file) on such a zpool / vdev setup (total capacity vdev A: 4 TB, total capacity vdev B: 8TB)? How does this file gets balanced accross the vdevs?
I think this is a usual problem, isn't it? Maybe, the drives of a vdev get replaced by bigger drives upon disk failure, which could result in vdevs having different total capacities within one zpool?
In very general terms, is it true to say, the more vdevs you have the higher will be your throughput? (because of more striping?) Do get files automatically striped accross all vdevs when adding additional vdevs? (Well, I think so because the loss of one vdev means the total loss of the zpool?).
Thanks so much for your help!
I'm still in preparation of building my first FreeNas system. While thinking of doing an all-SSD-based solution versus HDD-based-server following questions arised:
1.) - What happens when a zpool consists of multiple vdevs of different disk numbers and different disk sizes and even different RAID-levels?
2.) - What happens when a zpool consists of multiple vdevs, each vdev containing the same number of disks, however different disk sizes, same RAID-levels?
Example for 1.)
vdev A: 6x 6TB (RAID-Z2)
vdev B: 9x 1TB (RAID-Z3)
Example for 2.)
vdev A: 6x 2 TB (RAID-Z2)
vdev B: 6x 4 TB (RAID-Z2)
I'm especially interested in 2) because I'm thinking of starting a "small" FreeNas Server based on 6x 2 TB SSDs and add additional capacity by adding additional vdevs with bigger drives at a later point, when SSDs prices get cheaper.This would mean that I start with vdev A and add vdev B in maybe one or two years.
How is the striping-performance affected when each vdev is different in total capacity? How gets a file stored (e.g. 10 MByte file) on such a zpool / vdev setup (total capacity vdev A: 4 TB, total capacity vdev B: 8TB)? How does this file gets balanced accross the vdevs?
I think this is a usual problem, isn't it? Maybe, the drives of a vdev get replaced by bigger drives upon disk failure, which could result in vdevs having different total capacities within one zpool?
In very general terms, is it true to say, the more vdevs you have the higher will be your throughput? (because of more striping?) Do get files automatically striped accross all vdevs when adding additional vdevs? (Well, I think so because the loss of one vdev means the total loss of the zpool?).
Thanks so much for your help!