2x SSD Cache Devices are showing as 1x Cache Devices


Awkward

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Hello everyone,

 

I am currently trying out unRAID version 6.2, I am have a question in regards to Cache Devices. I have two VM running Windows 10 x64 1607 running stable at the moment, however, I noticed that under the Main tab of the server, two SSD 240G are showing as a single cache device, not two cache devices, with a pool of 240G, not 480G, is that normal? So, the second SSD is unusable or perhaps it is because I am using trial version, and it limits the amount of devices?

 

Kind regards.

 

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No this is normal.  By default the SSD's will have been set up in RAID1 mode to give redundancy which is why there is no observed increase in usable space.    It is possible to manually switch to RAID0 if space is more important than protection against failure (searching forum should find instructions on doing this).

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Re: Itimpi

 

Thank you for your response, I will keep it as RAID1, I think I would like to keep the speed over extra space. As for RAID0, I am going to read up on it more to understand more about it.

There is no speed improvement running it as it is now in RAID1. RAID0 in btrfs is not the same as normal raid 0 as far as I know. Its not writing to both devices but one of them.

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Re: Itimpi

 

Thank you for your response, I will keep it as RAID1, I think I would like to keep the speed over extra space. As for RAID0, I am going to read up on it more to understand more about it.

There is no speed improvement running it as it is now in RAID1. RAID0 in btrfs is not the same as normal raid 0 as far as I know. Its not writing to both devices but one of them.

 

Right, so, I am getting no improvement as is my setup right now, RAID1? Then should I just remove the secondary SSD and use it for something else?

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I wish it was made more clear that it would be raid 1 when adding a second cache drive. It would of saved a lot hassle for me.

 

There should be an option on the GUI to add a 2nd cache drive to just increase storage on the cache pool for those that don't want redundancy.

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I wish it was made more clear that it would be raid 1 when adding a second cache drive. It would of saved a lot hassle for me.

 

There should be an option on the GUI to add a 2nd cache drive to just increase storage on the cache pool for those that don't want redundancy.

Yes, sorry about that.  On the Main page, the 'Device' column is referring to a physical device.  When unRAID started out we only had a single 'Cache' device.  Later we wanted to offer redundancy in the cache so we added the ability to put multiple devices into a 'cache pool', using linux 'btrfs' file system to accomplish raid-1-like redundancy.  Since the Main page also displayed information such as the file system in use, free space, etc., we decided to use the 'Cache' line to display this information related to the pool.  But from the standpoint of physical devices, when you click on 'Cache' you are seeing info related to that specific device (such as SMART data).  When you click on 'Cache 2' you are seeing info related to the second physical device in the pool.

 

In btrfs turns out you can add as many devices to a pool as you want and still maintain raid-1-like mirroring, even if there is an odd number of devices - it just means each block of data is stored on 2 devices, btrfs chooses which 2 for any given data block.  This is why I call it "raid-1-like".

 

Right, in unRAID OS by default when there are multiple devices assigned to the cache pool, we format the pool using 'raid1'.  There are other possibilities: raid0, raid5.  A future unRAID-OS release will provide configuration capability for these other data organizations.

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