July 5, 20251 yr I've been using Unraid for a few months now, and I think it's safe to say I'm officially addicted.But there's still one question that's been nagging at me.Could someone explain to me like I'm five the difference between the cache and a pool (I'm not talking about the cache)?From what I understand: the Array is only for hard drives and it's slow, whereas the cache and a pool can be made up of SSDs (because speed).But if all the data goes to the Array (or the cache), then what exactly is the point of using a Pool?Is it just a spa for SSDs or is it actually useful?When and how should I use a pool instead of the array or the cache, and how do you get parity on a Pool (if that's even useful)?
July 6, 20251 yr Community Expert Solution cache is a general pc term meanind to put temperaly before saving...There are quite a few "cache" things.there memory cach, there disk cache, there IO Cache the Virtual Cache... would need more context then just the word cache...Unraid docs would help here:Storage Management | Unraid DocsStorage Management | Unraid DocsTo assign devices toShare settings as well...https://docs.unraid.net/unraid-os/manual/shares/https://docs.unraid.net/unraid-os/manual/shares/user-shares/https://docs.unraid.net/unraid-os/manual/shares/disk-shares/How to explain....Imagine your Unraid server is a house.The Array is your big, slow filing cabinet—great for long-term storage, but it takes a while to open drawers.The Cache is your kitchen counter—fast and easy to reach. You drop things there first before later moving them to the filing cabinet (the Array). Unraid does this automatically using the mover.A Pool is like an extra room in your house. It's not the kitchen counter (cache), and it's not the filing cabinet (array). It's just another space, and you decide what it's used for.So, what's the difference between a Cache and a Pool?Technically, they're both BTRFS/ZFS disk groups—what Unraid now calls pools. The only real difference is whether you assign a pool to act as a cache for the Array (via share settings like "Use cache: Yes/Only/Prefer")....So, when is a pool not a cache?When you're using it for:Appdata (for Docker/VMs) that should never move to the arrayDownloads (Deluge/qBittorrent/SABnzbd etc.) that benefit from SSD speedMedia (e.g. 4K videos for Plex) that you don't want slowed down by the ArrayBackups, scratch disks, or ISO libraries that don't need parityBut what about parity for pools?Pools don’t have Unraid-style single parity.But BTRFS pools can be mirrored (RAID1), striped (RAID0), or more (RAID5/6 with caution).Want redundancy? Use RAID1 or RAID10 for your pool.Want performance? Use RAID0 (no redundancy).Summary...Cache = fast temporary space for the array.Pool = fast permanent space you can use however you want.Both are “pools,” just used differently. Cache is a role, not a thing.
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