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Duplication File Write/Read Method with SSD/HDD Pool


ballardian

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I'm curious how DP manages the duplication writes to 2 disks in a pool.  For example, if I had an SSD and a HDD in a pool does DP write a file to both and wait for both to finish to move on. Or does it have separate queues where the SSD will be done 'first' while the HDD is still writing?  In either case I expect DP to report the slowest write time as the Windows progress bar/time/done.

This also would apply with an SMR drive paired with a CMR drive. 

To be clear I'm not expecting the SSD to make any writes to DP faster just curious if any part of a faster disk paired with a slower disk is taken advantage of at all.

Reciprocally, I understand DP uses both drives for read which in theory could speed up an SMR drive and slow down an SSD.  In a very ideal world only the SSD would be used to read. Though I believe this isn't possible to assign a primary 'read' drive in DP. Is that correct?

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12 hours ago, ballardian said:

I'm curious how DP manages the duplication writes to 2 disks in a pool.  For example, if I had an SSD and a HDD in a pool does DP write a file to both and wait for both to finish to move on. Or does it have separate queues where the SSD will be done 'first' while the HDD is still writing?  In either case I expect DP to report the slowest write time as the Windows progress bar/time/done.

I recently added a SSD to the front end of my DrivePool. What I have observed, is that all file transfers to both duplicated and non-duplicated folders are first written to my SSD which I have set up automatically balance when there is 100 GB to be moved. So the file transfer, on my system, just writes the files to the SSD and not to a SSD and HDD at the same time to folders with duplication. DrivePool reports the write speed to my SSD.

When a SSD cache flush is triggered, it is done in the background and the DrivePool GUI does not report the transfer speed. I have to go into Task Manager to look at the data being written to the HDDs in the background. Currently, my DrivePool is transferring files in the backgound on my computer. The DrivePool GUI reports no disk activity, but it does show "Balancing" in the task bar. Task Manager reports background data being written at 60 MB/s from my SSD to my USB 3.0 HDD (5900 rpm).

I have very few folders tagged for duplication, so I just let DrivePool duplicate the required files in the background when it does its maintenance routine. You can trigger a duplication check manually by going to Settings>Troubleshooting>Recheck duplication.

12 hours ago, ballardian said:

Reciprocally, I understand DP uses both drives for read which in theory could speed up an SMR drive and slow down an SSD.  In a very ideal world only the SSD would be used to read.

You can check the option for "Read Striping" like you said, and DrivePool will read from 2 HDDs in an attempt to speed up file transfers. When transferring reads from a duplicated folder, I notice the file transfer starts off slowly as it appears to access both copies and starts to read the files. Within a few seconds, it looks like DrivePool recognizes the faster drive and uses that for the bulk of the data and the slower drive is accessed much less. My total read transfer rate with read stripping (duplicated folders) is faster than the signal fast drive with a copy. 

I think most people use a SSD in DrivePool as a front end cache. If a duplicate file is still in SSD cache, then I only have one copy, and the transfer read rate is that of my SSD capability. If DrivePool has flushed the cache, then both copies of the file(s) are the archive HDDs. I cannot think of an instance on my system where I would have 1 copy in SSD cache and 1 copy in archive HDD.

14 hours ago, ballardian said:

Though I believe this isn't possible to assign a primary 'read' drive in DP. Is that correct?

I think that's right. I have yet to see any checkbox to assign a primary "read" drive in DrivePool.

If you really need to transfer files around as fast as you can, then set your SSD cache to a higher amount so DrivePool does not trigger a re-balancing and instead retains the data in SSD cache. I will sometimes manually request a DrivePool balancing (to flush the SSD cache) and then use my empty 100 GB SSD cache for temp and working files with some programs. When I do hit a trigger point on my SSD cache, then DrivePool flushes everything on the SSD out to the archive HDDs.

There is also a program called Primo Cache which lets you set both a RAM cache and a SSD cache. That can significantly speed up some file transfers, for both reads and writes. It may be one way to force a cache primary "read" drive in not only DrivePool, but across your whole computer system. Last time I checked Primo Cache still had a trial period where you can use the software to see if it meets your needs.

If you are still considering getting into DrivePool, all I can say is that it really works great for me. I use DrivePool as my media storage center for Plex/Kodi and super high speeds are not my main concern. Having said that, with my new SSD on the front end of DrivePool, I can get transfer speeds of ~130 MB/s with real data and CrystalDiskMark writes of ~430 MB/s with their test data.

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