Am I understanding correctly that if I have a pool, and it consists of 2x vdevs of mirror types, than
if one of the mirrors fails then I lose all the data right?
So if I want to reduce the potential damage in this scenario - I should create two pools and each should have its own mirror - and nothing else. Right - then if one of the mirrors suffers castrophic failure - i end up with 50% of data intact (assuming pools are equal in size), the downside is that the filesystem structure is more annoying. right?
I’m wondering what should I pick as a newbie for easy of operation and easier/cheaper upgrades. I have 6 SATA ports, I bought 2x16TB drives and in the future I’m planning to buy another set. Two free SATA ports in this scenario would be used for resilvering if one of the mirrors gets old. Does that sound like a sane strategy?
Your are right, if you have a pool with 4 disk consisting of two 2-way mirrors striped together, each vdev (and the pool) survives one disk failure. If two drives in the same vdev in this scenario fail, the whole pool is gone.
You could set up 4 disk in a raidz2, than any two disk could fail, and you could add more disk later via raidz-expansion.
Given the disk size (hopefully not SMR), a raidz1 is not recommended. Resilvering takes long and stresses the drives, and a second failure would destroy the pool in a raidz1.
Well, if you have two disk now and buy two disk later, then going for two mirrors with separate pools or striped into one pool, are a valid strategy.
This is as much about data protection as about accessabilty.
If you stripe two disk, the data is not accessible while you restore from backup.
If you mirror two drives, you loose capacity but when one disk fails, but you can still access the data while resilvering (leaving other data protection features of zfs aside).
It really depends on how much accessability and data protection you need. That is for you to decide.
Yep, obv you need 4 disk despite in mirror 2 are enough. But with a pool of mirror vdev, you have the capability to mix differents disks size for each vdev (Eg 2x16 + 2x20).
Or you can start with your mirror vdev now, and then in future ricreate the pool as a raidz2, with the new disks you will buy, and should not be too much tricky (like degrading the mirror removing 1 disk >> create a degraded raidz2 pool with 3 >> move data from mirror >> add the last disk to the new pool >> rename the pool).
If you’re considering a stripe of two (2-way) mirrors, you’re starting from four drives… which is exactly what you need for raidz2. So same price, same capacity, lesser performance with 4-wide raidz2 (IOPS), and lesser flexibility (can’t remove vdevs, though now you can increase width through raidz expansion) but arguably better resiliency with raidz2 (can lose any two drives).
Your call. Mine would be for raidz2 (“safer”).
Yeah I would be a bit affraid to use pool with 2 striped mirrors.
I will have just 1 pool with 1 mirror - and if I run out of space in the future I plan to add 2nd pool with additional mirror.
