Cache drives

[kcgodwins]

New here.

 

I've got FreeNAS up and running right now; I installed it over the weekend and my opinions on it are mixed.

As part of my NAS building project, I had always intended to try FreeNAS and UnRaid to see which I liked better; well now it's UnRaid's turn.

As noted, I have a working system, but what it does not have - and what I had previously read somewhere it really should have for unraid - are cache drives.  My intent was to install a couple SSDs (250GB each if that's big enough) but after reading around a bit, I'm not seeing anywhere where SSDs are mandatory and I'm now wondering if I should go with them or traditional SATA hard drives.

 

Does anyone have an opinion on this and would like to share?  Whichever I choose, I'm going to go with a 2.5" form factor, if that makes any difference.

 

Thanks in advance.

Mike

[trurl]

In addition to caching user share writes (not important for everyone), cache is often used for other things where speed gains are important. Installation of applications (dockers) and Virtual Machines are the most obvious examples.

[tdallen]

2 hours ago, kcgodwins said:

As noted, I have a working system, but what it does not have - and what I had previously read somewhere it really should have for unraid - are cache drives.

The internet tends to remember things forever.  Sometimes that's good, sometimes that's bad.  In this case it was definitely a "thing" years ago to run unRAID with cache drives for the purpose of caching writes to the parity protected array.  At the time hard drives were performing at 50 MB/s and writes to the array were 10-20 MB/s.  These days drives are performing at over 160 MB/s and with unRAID turbo write enabled, writes to the array can be well over 70 MB/s.  But unRAID shall forever be known as an OS that needs write caching, sigh . 

 

As trurl mentions, the primary use of the cache drive today is as the defacto application drive for Dockers, VMs, etc.

[kcgodwins]

Have the NAS up with Unraid now, worked on it for a few days to get everything precleared and whatnot, was able to start putting data on it yesterday.

 

I currently don't have cache drives but it's something might want to add down the road.  So far, however, I'm loving it.  Getting plex running in a docker was a no-brainer and it "just worked".  I cannot say the same for Freenas.

 

Thanks for the input earlier.

 

Mike

[HellDiverUK]

My main use of a SSD cache on unRAID is for speedy Plex library browsing.  If I weren't needing that, I'd likely just use a 2.5" 7200rpm HDD.  I prefer having a cache drive because it means the main array drives can stay spun down for the longest time.  For example, most days the main drives only spin for an hour while Mover clears the cache drive to the array drives.