Hi, new to TrueNAS/ZFS and seeing that when I created my DRAID pool, it says to use a power of 2 number of drives. Currently, I only have 14 drives and so would need to purchase 2 more to get to 16. Do I need to do this now or can I add them later. Also, I selected 3 drives for redundancy. Is the 3 counted in the power of 2 requirement or is 16 the total I would need?
On average, the files I will be storing are around 250MB. Does this impact what I should do? I would like to maximize my storage capacity (while keeping the 3 drive redundancy).
I would argue that 16 disks is not nearly enough to go for draid… it would only make sense for 20 to 100 disks… And i don’t even know if you can expand a draid pool with raidz expansion…
Thanks…maybe a silly question, but I thought it was best practice to limit the number of drives to be less than 20? I’m sure I’m confusing concepts here.
No, you can not add columns to ZFS’ implementation of dRAID vDevs.
This is for RAID-Zx vDevs. At some point it makes more sense to add a new RAID-Zx vDev than to add columns. The working rule is about 12. Going to 13 or 14, (for RAID-Z2 or Z3), is not bad per say.
However, having 18, 20 or more disks in a single RAID-Zx vDev puts things on the edge. Large files will span all data columns, which can cause resilvers to take longer.
This can also impact usability due to fragmentation of free space. Even to the point of the pool getting slower over time. With the only fix being “backup, destroy, re-create with more sane values, and restore data”. Making maters worse, people wait until the pool is so slow, they have to do something. Except by then, backing up is a real problem because of the slowness.
