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Is there a way to disable write caching for Covecube Virtual Disk?


Tarh

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Hi, so I'm experimenting with DrivePool and it seems to be using write caching even if the individual drives in the pool have it disabled, basically overriding it.

But for the Covecube Virtual Disk driver there's no Policies tabs in Windows' Device Manager so write caching can't be disabled.

 

The problem I have is that writing files to the pooled drive says it's done within seconds with inaccurately high speeds (due to caching) but I can see the actual speeds of each physical drives and they keep writing in the background even minutes after the writing was supposedly completed. Same even on SSDs. I want to see the real progress of writing the files, without extra caching, not just a promise of it being done soon in the background.

The caching also screws with tools like HD Tune Pro claiming the read speeds are around 6 gigabytes/second for a pool with 3 SATA drives. It's basically a small built in RAM drive.

I get the massive benefit of caching but I don't want it for my usecase and wondering if it can be disabled. Thanks.

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Out of curiosity, exactly what is your use case?  Why do you need to measure uncached read/write speeds on a virtual drive?  I know it's an inconvenient hack but you could aggregate perfmon throughput stats for individual disks if you really need to.  Otherwise, you might get some mileage out of a nice Powershell script.

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I don't need to measure the real speeds, I want to write without caching. I just noticed it while testing before deciding to go with the software or not.

I don't like caching because of potential data loss. Just checked and after pushing some files to a HDD pool of two, 4.7 GB of actual data was written after it says the copy was done at ~900 MB/s reportedly, while the monitored real speed was ~100 MB/s to a single HDD (the other had much less free space so it wasn't used). That's 4.7 GB of data "on the fly" in RAM for 47 seconds that would get lost in case of a power outage. And then you'd have to check all the target files because they were all preallocated and many of them were being written simultanously from the cache. Meanwhile, without write caching and a power outage only one file would be cut off (which you could easily spot or it might not even exist, and stay marked as free space) that was actually in the process of being written and the rest wouldn't exist yet on the target.

For me there's no reason to have gigabytes of data on the fly just to have some inaccurate speed spike in the beginning of writing tens or hundreds of gigabytes of data and to have them finish in the background minutes later hoping a power outage/bsod doesn't happen.

If caching can't be disabled because of how the software works, I'm hoping for a user option to reduce the size to a custom value.

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On 1/7/2019 at 8:18 AM, Tarh said:

But for the Covecube Virtual Disk driver there's no Policies tabs in Windows' Device Manager so write caching can't be disabled.

Write caching wouldn't affect the Pool drive, since there is no data actually being written to it.  All of the activity is actually redirected to the underlying disks.  So the write caching settings on those is what matters. 

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That is exactly what I would have thought logically, but believe me I wouln't have waste my time registering only to waste everyone else's time making a post before testing it thoroughly.

You can easily check it yourself how the write caching option for the individual drives added to a pool is being ignored. Just try making a pool of 2 HDDs, push a few gigs of files, preferably from an SSD or even faster source and watch the initial write speeds. Or watch resource monitor and the actual write speed of disks *after the copy has been reportedly finished*. Or try HD Tune or other disk benchmark tool that doesn't circumvent the issue (no CDM). ~900MB/s reported initial copying speeds by windows or total commander or 6 *gigabytes/second* of benchmark reading speeds with HD Tune Pro are not at all real when it comes to 2x7200rpm HDDs.

I don't know exactly but I'm guessing the nature of the low level virtual disk driver overrides OS caching options completely. Or in other words, it has it's on cahing on top of the OS write caching. My problem is, the cache is way too big (at least 4.7GB in a system with 64GB of RAM). This is the only thing preventing me from buying the software.

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