SSD Cache Limitations ?

[Vishesh Gupta]

I would like to build a Home Storage Server,

 

5 x 8TB WD Red Drives (1 drive for parity, 4 for storage)

1 x 500GB SSD For cache

 

I will be using my Macbook Pro as Plex Server, with the Unraid Server selected as Storage Location. 

 

1) What is the recommended Rack Server Build Specs I should go for. 

2) I won't be keeping the server on 24hours a day, would turn the server on only when I want to use Plex or dump some data onto the server. Which would be typically 2 to 3 hours a day. My main query is, how long does it take for the server / array to restart everytime I boot, assuming 32TB of used disk space. 

3) Lastly, I would like to know the transfer speeds. I have read across forums that the transfer speeds are about 40MB/s on a Gigabit ethernet connection, things speed up to about 100MB/s if we use SSD for cache. However, the data that is dumped to the SSD gets transfered to the drives at a fixed time in a day, is it possible that the data gets transferred from SSD Cache Drive to the HDD drives just after a minute ?

4) I will be having a 500GB SSD for Cache. Once I build the server, I would like to dump around 25TB of data onto it. If I transfer more than 5TB at a time, what are the limitations of the cache drive, and is there a work around it?

 

[NewDisplayName]

1.) doesnt matter, depends on your budget and what you wants

2.) is possible, but usually not suggested if server is doin nothing it wont use more then some watts (my build, and all routers around it, take 70watt when doin nothing)

My bootup take less then 5 min - 35tb.

3.) i have full 1gbits and i use cache drive, you can script everything what you want with user scripts, i .e.g let it run every 15 min if there is less then X% on cache free.

4.) speed will be probably around 50-100mb/s after cache is full, you can enable turbo mode, where you should get around 100mb constanly.

[pwm]

On 7/20/2018 at 7:07 PM, Vishesh Gupta said:

I will be having a 500GB SSD for Cache. Once I build the server, I would like to dump around 25TB of data onto it. If I transfer more than 5TB at a time, what are the limitations of the cache drive, and is there a work around it?

Don't fill the system using a cache drive. It isn't faster to first copy to the cache drive, then move the data to the array then fill more to the cache.

 

Turn on turbo write and you may get transfer speeds close to the speed of the gbit network interface. It is when unRAID uses read/modify/write for parity (which means it's enough to have just one data disk + parity spinning) that you get really slow write speeds because the drives needs to do a read and a write for every block saved to the array.