Array setup


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44 minutes ago, frodr said:

Thanks,

 

If I get antoher 2 TB drive, can I then run 3 parity and 20TB unformatted?

No. Unraid allows either 1 or 2 parity drives, both of which must be same size or larger than any single array drive. All data drives are fully usable. The reason I state unformatted is that some people don't get that the filesystem itself takes up space on the drive, so a 4TB drive will have around 4GB used by the format if you select XFS. I don't know what the typical overhead is for BTRFS.

 

If you add a 2TB drive to either of the scenarios I laid out, you would have 20TB or 10TB raw capacity available. Simply add all the data drives together to get raw capacity, as each drive is independently formatted, and you can mix formats or encryption as you see fit.

 

The "extra space" of a larger parity drive is wasted, the only reason to use a larger drive is to allow adding that size drive as an array data member at a later date without having to change the parity drive at the same time.

 

 

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3 hours ago, frodr said:

What are the general recommendation regarding cashe drives? Big as possible? Does many drives change anything? I have up to 4 x 1TB SATA ssd`s. I have 2 x M.2 512GB PCIe ssd`s which I can add on a PCI card. 

 

// Frode

Cache pools use BTRFS RAID levels, RAID1 is selected by default, you can manually force other levels. Mixing different speed and capacity devices in the pool will typically limit the pool by the slowest or smallest device.

 

See here for a calculator to show what free space will result from different RAID options.

http://carfax.org.uk/btrfs-usage/

 

Space needed depends entirely on usage. The cache pool is typically used to permanently keep VM and docker settings and executables, and as temporary space for new writes at the highest speed possible.

 

It's not utilized as a read cache for the array, write only.

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