SSD CACHE DRIVE in RAID

[tessierp]

Hi,

 

I was thinking of using a SSD in a UNRAID system to accelerate saving data to the NAS but was wondering if any of you are using two SSD in RAID mode to make sure that in case an SSD fails, data wouldn't be lost until the files are transferred to one of the HDDs. Is anyone doing this? Is it worth it?

 

Also, how slow is an UNRAID system if you do not have an SSD cache drive, what are the typical read / write speeds over a network? In other words, what is the best possible performance without an SSD cache drive? I will be using a DELL PERC H200 and WD RED 6TB NAS HDD with 256 MB CACHE on each.

 

Thanks

[JorgeB]

13 hours ago, tessierp said:

Is anyone doing this?

Many are.

 

13 hours ago, tessierp said:

what are the typical read / write speeds over a network?

Depends on the hardware and write mode, with turbo write, fast disks and no bottlenecks you can get 200MB/s+.

[tessierp]

10 hours ago, JorgeB said:

Many are.

 

Depends on the hardware and write mode, with turbo write, fast disks and no bottlenecks you can get 200MB/s+.

 

It is not that bad if write operations are not critical and can skip on the initial deployment by not adding a SSD for caching.

 

I don't think I would go with just a single SSD but two in RAID to make sure there is no loss of information.

[trurl]

1 minute ago, tessierp said:

It is not that bad if write operations are not critical and can skip on the initial deployment by not adding a SSD for caching.

If you enable Docker or VM Manager in Settings without a cache drive installed, those will get created on the array and it will take multiple steps to get them moved to cache where they need to be so dockers/VMs perform better and don't keep array disks spunup.

[tessierp]

37 minutes ago, trurl said:

If you enable Docker or VM Manager in Settings without a cache drive installed, those will get created on the array and it will take multiple steps to get them moved to cache where they need to be so dockers/VMs perform better and don't keep array disks spunup.

I'm not sure I understand. You mean that if I do not use a SSD drive for caching, to use Docker / VM manager will actually accelerate the writing of data to the UNRAID array?

[trurl]

  

49 minutes ago, tessierp said:

You mean that if I do not use a SSD drive for caching, to use Docker / VM manager will actually accelerate the writing of data to the UNRAID array?

No that is not at all what I mean.

 

The user shares for dockers/VMs (appdata, domains, system) are normally cache-prefer, so they will be created on cache and stay on cache if there is room. Having these on cache allows dockers/VMs to perform better since cache isn't impacted by slower parity updates, and cache is often SSD so even better performance.

 

If you have no cache, these will get created on the array. In addition to not performing as well on array, dockers/VMs always have files open on these shares, so array disks can't spindown if these shares are on the array.

 

Mover moves cache-prefer shares to cache when there is space, so after you install cache they could be moved there. But Mover can't move open files, so Docker and VM Manager have to be disabled before they could be moved. So, multiple steps to get these moved to cache if you let them get created on the array.

[tessierp]

3 hours ago, trurl said:

  

No that is not at all what I mean.

 

The user shares for dockers/VMs (appdata, domains, system) are normally cache-prefer, so they will be created on cache and stay on cache if there is room. Having these on cache allows dockers/VMs to perform better since cache isn't impacted by slower parity updates, and cache is often SSD so even better performance.

 

If you have no cache, these will get created on the array. In addition to not performing as well on array, dockers/VMs always have files open on these shares, so array disks can't spindown if these shares are on the array.

 

Mover moves cache-prefer shares to cache when there is space, so after you install cache they could be moved there. But Mover can't move open files, so Docker and VM Manager have to be disabled before they could be moved. So, multiple steps to get these moved to cache if you let them get created on the array.

Thanks for explaining this to me.. Appreciate it. I will most likely not run any docker containers on my UNRAID unit. I already have two dedicated machines running Proxmox where I have my VMs and some docker containers on them. I intend to use UNRAID purely as a NAS but I may still add one SSD for caching.