Replacing SSD Cache drive with RAID 0 SAS drives, 600 GB, 10K HDDs, any disadvantage to this?

[jang430]

Hi.  I am running out of space on my cache drive, 1 TB SSD, since it is also being used as a drive for a gaming VM.  I'd like to change it to unassigned drive.  Rather than replacing cache drive with another SSD, I have several unused 600 GB SAS 10K, 12 Gbps HDDs.  Is there a downside to using this rather than getting an SSD?  

 

Any upside to it as well?

 

I remember the time when I had an old HDD as a cache drive before moving to SSD, boot up times, or starting of docker container, took it's sweet time.  Will using RAID 0, and using drive described above, bring me back to the olden days when it took a long time to have docker apps automatically started? 

 

I have a Dell Perc H310, flashed with IT mode.  To use Raid 0, do I need to reflash it?

 

With just 1 SSD as cache drive, my drive always show as unprotected, since it's a single drive.  What kind of RAID level if using SAS, will show as protected?

 

 

[JorgeB]

31 minutes ago, jang430 said:

Is there a downside to using this rather than getting an SSD?  

Slower?

[CS01-HS]

I've run 3 drives in a secondary RAID 5 pool since about beta-25, so far so good.

It shows as protected on the Shares page.

 

I'd worry about speed with appdata.

Doesn't hurt to try?

*Sometimes it hurts to try.

 

[JorgeB]

I also have a few HDD based raid pools, and depending on what you're going to use them performance can be good, like for reading or writing large files, it's just never has good as an SSD for IOPS.

[jang430]

Thanks. So will consider Raid 5.

I was kind of hoping with Raid 0, it will somewhat be comparable to Ssd. I wonder if Raid 5 will improve speed. Will read about it.


Sent from my iPhone using Tapatalk

[jang430]

A follow up question, since sas cache won't match ssd performance, does docker apps need to be in cache? I don't mind the cache being slower, so as long as docker apps start as quick as possible when you boot up unraid.


Sent from my iPhone using Tapatalk

[CS01-HS]

I have no experience with 10K SAS drives but RAID 0 or RAID 5 will be faster than the array which is limited by the speed of a single drive, so you're better off with docker apps in the RAID pool.

 

I forgot to mention in my other post - no reflashing. You format the pool as BTRFS and set the RAID level with the web GUI (software.)

[jang430]

Thank you for the clarification on the HBA controller- no flashing. 

 

As for the docker apps, yes, I know the cache is way faster than the array primarily due to not going through the Parity.  My concern though is how slow does the apps load in RAID 5 SAS drives as cache? I think I'll have to check to find out.  

 

Does docker apps have to reside in cache?  

[CS01-HS]

I think a cache drive is optional and if so, no, they can run from the array.

 

Here are instructions for replacing your cache pool but they may not be current so search to confirm:

https://wiki.unraid.net/Replace_A_Cache_Drive