TrueNAS-SCALE-22.12.3.2: I have a pool consisting of 4 x 14TB drives (mirrored)- they are identical and all seems fine. If I want to expand the pool, can I add, for example 2 (or even 4) identical (to one another) 6TB drives, or am I stuck with only being able to add 14TB drives from now on?
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Mixing drive sizes in a pool
- Thread starter rtX
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Yes, you can add a pair of 6TB drives as a Mirror vDev. Or even 2 pairs of 6TB drives in 2 Mirrored vDevs.
Performance may be irregular because ZFS will tend to favor the vDev with the most free space. Then, when the vDevs are balanced, (if ever), then ZFS will stripe across the vDevs equally.
PS what I meant by "if ever", is that some NAS installations are storing archival data that does not get updated. Thus, it sits where it was originally written. You can manually re-balance after adding or removing storage, but that is not perfect.
Performance may be irregular because ZFS will tend to favor the vDev with the most free space. Then, when the vDevs are balanced, (if ever), then ZFS will stripe across the vDevs equally.
PS what I meant by "if ever", is that some NAS installations are storing archival data that does not get updated. Thus, it sits where it was originally written. You can manually re-balance after adding or removing storage, but that is not perfect.
WI_Hedgehog
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The other consideration is how many free ports are available for hooking the drives to. If they're SATA you'd need 2 or 4 free ports (presumably on the mainboard), if SAS the HBA would need to have those ports available on the card.
Given at least one port "somewhere" is used for a boot drive that could mean you have 1 or perhaps 3 open ports.
Given at least one port "somewhere" is used for a boot drive that could mean you have 1 or perhaps 3 open ports.
Thanks @Arwen and @WI_Hedgehog. I have a couple of 8 port HBA cards hooked up to a 16 port backplane. Boot and a couple of other drives are linked via the ports on the mainboard, so port numbers are not a major issue.
The balancing consideration is one that I'll have to consider. Most of the data will be static (uploaded once and the accessed infrequently), and the files are for the most part large (in excess of 100GB). I'll look at manually rebalancing, but fear that the large files will just end up being fragmented.
The interface to the NAS will be relatively slow (ethernet) and so I think that is likely to be the performance issue rather than the way the data is stored. Is there any reason that I *should* do a manual re-balance - I presume that you do this by copying the data and deleting the old copy?
The balancing consideration is one that I'll have to consider. Most of the data will be static (uploaded once and the accessed infrequently), and the files are for the most part large (in excess of 100GB). I'll look at manually rebalancing, but fear that the large files will just end up being fragmented.
The interface to the NAS will be relatively slow (ethernet) and so I think that is likely to be the performance issue rather than the way the data is stored. Is there any reason that I *should* do a manual re-balance - I presume that you do this by copying the data and deleting the old copy?
WI_Hedgehog
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Fragmentation is a known part of a Copy On Write filesystem. The FS attempts to minimize fragmentation, so as I understand it fragmentation is generally not an issue until a lot of deletions happened and the vdev is over 75% full. Fragmentation seems to be a trade-off for increased data integrity.
Excessive fragmentation in a large file can be an issue as it causes slower data retrieves and drive wear. For corporations that replace servers on a five-year schedule this is a self-rectifying situation, home users might be running 10 or 15 years on limited (affordable) hardware and fragmentation can be a bigger issue. In this case I think poor system design is a greater factor and home users could use more understanding of why their system is bottlenecking.
In your case I think you should be fine as the fragmentation level should be minimal given files aren't usually rewritten.
Excessive fragmentation in a large file can be an issue as it causes slower data retrieves and drive wear. For corporations that replace servers on a five-year schedule this is a self-rectifying situation, home users might be running 10 or 15 years on limited (affordable) hardware and fragmentation can be a bigger issue. In this case I think poor system design is a greater factor and home users could use more understanding of why their system is bottlenecking.
In your case I think you should be fine as the fragmentation level should be minimal given files aren't usually rewritten.
