I'm starting to build my first unRaid server, and I know there are a few types of drives,(parity, storage, cache, and I also heard of an apps drive, but I may be mistaken).  I'm using a new WD 3TB Red drive for my parity drive, storage drives are a mixture of mixed size  green/red drives from my existing  WHS2011 system.  Is there a spec(7200 vs 5400/5900, or even an SSD) drives that are suggested for the cache and apps drive?  Is the cache and app drive the same drive? What is the suggested size for app and cache drives?

For this iteration, I'm using unRaid as strictly a media server, won't be running dockers( I think that's what apps are called), except for the UPS tie-in (apcUPSD), I'm still going to be running my WHS server for my torrents and Win programs that I need to run.

I should also mention that my plan is to build a second backup server to backup the media from the main media share on a monthly basis, so there may need to be another program(rsync), not sure if that needs anything special with the drives to help with the backups.

 

People generally use the same drive for cache and apps.  Drive type is up to you, as your use will dictate what you need.  I have a 1TB 7200 RPM drive for my cache.  If I ran a bunch of dockers or apps on unRAID I would consider running a SSD.

I don't cache writes to the array, but have an SSD cache drive for apps because it is simpler to let unRAID manage the drive. If you have a separate apps drive then you will have to do a little extra yourself to use it.

 

If you intend to cache data then you will need your cache to be large enough to hold as much as you intend to write before mover moves it to the array. The default mover schedule is daily at 3:40 am.

 

Faster is better but for writing your network may be the bottleneck. SSD is good for apps because a lot of the access is not over the network, and also apps will keep a spinner spinning.

 

 

You mention you don't cache writes to the array, I see the benefit of this once the system is up and running(if I have it right, I think it's to allow the system to build the parity in off times, keep the sever load lower.  How do you turn the option on and off to cache writes to the array?  Is it by having or not having a cache drive?), but at the beginning, when I'm trying to load the 5TB of data on it, I'd like to get the data onto it as quickly as possible.

Are there any guides or instructions on how best  to load the server with data when you first start?  I'm planning on using USB3 drives to transfer the data instead of the network to  allow me to move the data at night and not take up my WHS server load or network capacity when we are watching shows, etc.

In general, one of the benefits of the cache drive is you aren't waiting for the parity drive to write.  When you are first starting to build the array, you should simply not configure the parity drive and copy everything you need to, then configure the parity drive.  Aside from that, the process to copy data to the server is the same once parity is enabled.

The reason to cache writes is because it is faster. unRAID always maintains parity when writing the array disks. It does this by reading the disk to be written and reading the parity disk, then calculating what change the new data will make to parity, then writing the data disk and writing parity. So 2 reads and 2 writes for a write to the array. A write to cache is just a write. unRAID will later move that cached data to the array "when you aren't looking" so the slowdown won't be so noticeable.

 

As mentioned, people often wait until after the initial data load is done to add a parity drive. Then you will just be doing the one write. And parity would be completely built from scratch (several hours) when the parity drive is added.

 

Each user share is configured individually on whether to use the cache disk or not. Writes directly to a disk will not use cache. Note that any folder at the top level of cache or any array disk is automatically a user share whether you set it as one or not. If you don't configure a share it has defaults.

 

It is also possible to make a share stay on cache by setting it to cache-only. This is usually how people configure the share used to keep any application working data on.

 

If you want to transfer data from USB3 instead of over the network then you will have to get unRAID to mount the USB drive. Search for the SNAP plugin for help with this.

Thanks for all the help, I'm looking forward to firing it up this afternoon and starting the preclear