I was wondering if RAM memory requirements for ZFS are a function of raw drive capacity or useable drive capacity? And does the answer depend on RaidZ2 versus 3-disk Mirrored vdev’s?
For example, I’m planning on using 3-disk mirrored vdev’s. I’ll add drives in sets of 3 per vdev (so can survive up to 2 drive failures). For example:
vdev1:
3*6TB = 18TB raw storage, but only 6TB useable storage
Then I’ll add more vdev’s later as needed. So the total storage for this approach would be:
raw storage = #vdev * (3 * #TB)
useable storage = #vdev * #TB
Looking at this link (“How Much RAM is needed?”):
http://www.freenas.org/whats-new/20...design-part-i-purpose-and-best-practices.html
it mentions “8GB of RAM will get you through the 24TB range. Beyond that 16GB is a safer minimum, and once you get past 100TB of storage, 32GB is recommended.”
So is “24TB range” referring to raw or useable storage? And does a 3-disk Mirrored vdev solution like above require less/same/more RAM than RaidZ2 would for a given amount of useable storage?
For example, I’m planning on using 3-disk mirrored vdev’s. I’ll add drives in sets of 3 per vdev (so can survive up to 2 drive failures). For example:
vdev1:
3*6TB = 18TB raw storage, but only 6TB useable storage
Then I’ll add more vdev’s later as needed. So the total storage for this approach would be:
raw storage = #vdev * (3 * #TB)
useable storage = #vdev * #TB
Looking at this link (“How Much RAM is needed?”):
http://www.freenas.org/whats-new/20...design-part-i-purpose-and-best-practices.html
it mentions “8GB of RAM will get you through the 24TB range. Beyond that 16GB is a safer minimum, and once you get past 100TB of storage, 32GB is recommended.”
So is “24TB range” referring to raw or useable storage? And does a 3-disk Mirrored vdev solution like above require less/same/more RAM than RaidZ2 would for a given amount of useable storage?