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Slow Writes - SSD Optimizer not prioritizing SSDs


Andy2

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I'm running the 2.2.3.938 beta (latest version) and am experiencing issues with the SSD Optimizer Plugin.

The only balancer enabled in DrivePool is the SSD optimizer.

I have a 512GB SSD configured as an "SSD" in the plug-in, with all other drives configured as "archive".

 

File placement settings are configured so that:

"File placement rules respect real-time file placement limits set by the balancing plug-ins" is enabled, and "Balancing plug-ins respect file placement rules" is disabled.

Based on these descriptions, that should force all files to be written to the SSD before being moved off the SSD by rebalancing.

 

Instead, files are still following the placement rules that are set, and being written to slow HDDs - sometimes even my lowest priority "archive" disks (SMR HDDs) - rather than all writes happening on the SSD.

I have tried other combinations of settings but nothing seems to work other than adding the SSD to the placement rules, or removing the rules for that directory. Then the writes immediately start happening on the SSD.

But I don't want the files to live on the SSD, and folders which have file placement rules are done for a specific reason; e.g. files where faster access is required are placed on my fastest HDDs, while files that access speeds don't matter are placed on slower drives.

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Are you using duplication? 

If you are, and only have one "SSD" drive here, then that's the problem.   It writes duplicated data to both drives, in parallel.  if there are not enough "SSD" drives, then it will fall back on the archive drives, and slow down the writes.

 

Also, to make sure, this applies only to new files, and not modifications of existing files, unless they're on the SSD. 

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Just for my own edification Christopher - does that also hold true when you have a single SSD set as the optimizer drive, and real-time duplication is turned off?  Is Drivepool smart enough to hold the single deferred copy of the file on the SSD only long enough to duplicate to the regular pool drives?

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18 hours ago, Jaga said:

Just for my own edification Christopher - does that also hold true when you have a single SSD set as the optimizer drive, and real-time duplication is turned off?  Is Drivepool smart enough to hold the single deferred copy of the file on the SSD only long enough to duplicate to the regular pool drives?

Mostly, yes.

If it's a new file, yes, it's smart enough, and will work correctly.  
But modifying a file.... it doesn't use the SSD for that. 

Also, the duplication happens at a specific time each day. So the file isn't protected for up to 24 hours.  Even longer if the file is open, as we cannot duplicate open files.  (one of the reasons we recommend not turning off real time duplication)

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On 8/30/2018 at 10:37 PM, Christopher (Drashna) said:

Are you using duplication? 

If you are, and only have one "SSD" drive here, then that's the problem.   It writes duplicated data to both drives, in parallel.  if there are not enough "SSD" drives, then it will fall back on the archive drives, and slow down the writes.

 

Also, to make sure, this applies only to new files, and not modifications of existing files, unless they're on the SSD. 

I have duplication enabled for some folders, but not the ones I was using in this test.

I was moving files from my boot drive (NVMe SSD) to the drive pool, not modifying files.

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18 hours ago, Andy2 said:

I have duplication enabled for some folders, but not the ones I was using in this test.

If that's the case, 

Was the SSD drive fill, or close to the limit for it (eg, at or past the red marker on the drive)

If so, that may be the cause, actually, and would be normal.

Otherwise, enable file system logging and reproduce the issue: 
http://wiki.covecube.com/StableBit_DrivePool_2.x_Log_Collection

Then open a ticket at https://stablebit.com/Contact and upload the logs there.

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