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Reallocated Sectors - Drive Latency


stephenkjohnson

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I have a home servers with a 500 GB internal HD and eight 2TB drives pooled using StableBit DrivePool (Drivepool is running on the 500GB internal drive). On my 500 GB internal HD StableBit Scanner is showing 2415 reallocated sectors. SMART warning is coming up for this drive but the warning says it is not predicting imminent failure. Recently I have been having a lot of latency issues when playing movies off the pooled drives. This used to not be an issue and only was noticeable in the past couple months. Even smaller 720P TV shows are having latency issues. It is not just large BluyRay movies. The latency is much less if I run the same movie file off an external hard drive that is not in the pool. I am thinking the latency issue is the 500GB HD but wanted to check with community first before I start replacing parts.

Thanks for your help.

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  • Are the eight 2TB storage drives internal also, or externally connected (eSATA, USB, etc)?  Do they share the same controller as your 500GB internal?
  • Are you using something like Plex to host them on the server, and if so do you have thumbnail generation turned on in Plex Media Server for your problematic libraries?
  • Have you checked the eight Pool storage drives for SMART/Surface/File System errors, and are they all clean?  Stablebit Scanner is useful for this, and has a free trial period.
  • When you say the latency is "much less off a non-pooled external drive", how much less?  Back to normal, or does it still exist in some amount?

Even without answering any of these questions, I would replace that 500GB internal as soon as possible.  Drives are many times more likely to die after they start reallocating large numbers of sectors.  And it's much easier to salvage the OS and data before they die than it is after.

The reason for the questions above however:  the controller could be having issues if it's both SATA/eSATA and handling all your drives.  Plex Media Server uses thumbnails off the C: (default install) location for seeking in movies, and to store other metadata.  Depending on your duplication settings, the pool could be having issues if it's reading from more than one drive in the pool at once, and one or more of them have performance problems.  And if you have an external drive (not in the pool) but still on the same external controller, it may be completely unrelated to Drivepool - it may be something to do with other hardware.  It could still be an issue with Drivepool of course, but I'd look at lower layers first (hardware, OS, etc).

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As an afterthought - try browsing into one of the hidden PoolPart folders on your Pooled data drives, find a movie to test, and open it directly from there (not from the DP-mounted Pool letter).  See what your latency is like for that scenario.

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All the 2TB drives are internal SATA off the motherboard. I do have two of them connected via a PCI Express expansion card since the board could only handle 6 of the drives. I do have one external 4TB hard drive that is in the pool that is plugged in via USB. I am using XBMC/Kodi for media. Thumbnails are on the client PCs. I tested the hidden pool folder and played the file in VLC as you suggested and still had latency in playing video. A 20GB blu ray would have to buffer every 30 seconds to minute. The external HD I played video files off of that I mentioned in the OP is not in the pool but attached to the server via a USB. I played an uncompressed Blu Ray from it on one of the client PCs and had no issues. I have StableBit scanner installed on the server and the 500GB one is showing the reallocation I mentioned and a drive in the pool has 321262 load cycle count on a maximum of 300000. These are the only things coming up in Scanner. All else show healthy.

I will replace the 500gb drive and see if that helps.

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16 hours ago, stephenkjohnson said:

I tested the hidden pool folder and played the file in VLC as you suggested and still had latency in playing video. A 20GB blu ray would have to buffer every 30 seconds to minute. The external HD I played video files off of that I mentioned in the OP is not in the pool but attached to the server via a USB. I played an uncompressed Blu Ray from it on one of the client PCs and had no issues.

That tells me the issue probably isn't with Drivepool, since accessing the media file through the hidden folder takes it out of the equation completely.

Best first action (that you're already taking) is to replace the drive with reallocated sectors.  Once that's done you can try playing back the same video from the hidden Poolpart folder (like you did before) and seeing if it's resolved.  If not, copy the video file out of the pool and into the root directory of each pool drive (so it's on the drive but not inside the Poolpart folder) and test it on each drive for latency issues.  It might help illuminate if any of the drives are problematic, or possibly if their controllers or cables are potential issues.

The load cycle count is an artifact of a drive spinning down, spinning up again, repeat ad-nauseum (it parks the heads every time).  The 4TB WD Reds I have originally had a bug in the firmware and did it regularly in my old NAS until I flashed them.  You might want to check the manufacturer on that drive and see if they have a solution for it.  It's not an immediate indicator that it's going to fail, but spin ups/downs on a frequent basis are rather hard on the drive's longevity.

The fact the USB drive plays without hitching may indicate it's a controller-based problem, which is where the outside-the-poolpart-folder test of each drive can help.  Some may hitch playing back a video, others may not.

Good luck - let us know how it goes.  :)  It's definitely a ghost in the machine.

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On 8/17/2018 at 8:42 AM, stephenkjohnson said:

StableBit Scanner is showing 2415 reallocated sectors. SMART warning is coming up for this drive but the warning says it is not predicting imminent failure. Recently I have been having a lot of latency issues when playing movies off the pooled drives.

Yeah, you definitely would! 

The reallocated sectors means that data has been mapped to "blank spare" spaces.  Which means when reading sequential data (according to the file system), the physical location on the disks may NOT be sequential, actually.  And this can (will) introduce a good deal of latency, depending on how much data is reallocated. 

This drive is not fit for active use.  It may be okay for cold storage, but even that's iffy.  

I would RMA the drive if it's under warranty. Or at least remove it from the pool, and replace it. (or put it on temp file duty)

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1 hour ago, Christopher (Drashna) said:

The reallocated sectors means that data has been mapped to "blank spare" spaces.  Which means when reading sequential data (according to the file system), the physical location on the disks may NOT be sequential, actually.  And this can (will) introduce a good deal of latency, depending on how much data is reallocated. 

The thing I found odd was that the reallocated sectors were on his boot (C:) drive, whereas the files he was getting latency playing back were on the Pooled drives (without any reallocations).  Perhaps a caching issue with temp files on C: or the way Drivepool uses the C: drive during pool access?

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56 minutes ago, Jaga said:

The thing I found odd was that the reallocated sectors were on his boot (C:) drive, whereas the files he was getting latency playing back were on the Pooled drives (without any reallocations).  Perhaps a caching issue with temp files on C: or the way Drivepool uses the C: drive during pool access?

In that case, I would guess that it's affecting the pagefile then.  As that works as basically "on disk memory", and could slow down the system. 

Also, if using something like plex, if it's transcoding and storing the temp files on the C: drive.... that would also happen. 

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3 hours ago, Christopher (Drashna) said:

In that case, I would guess that it's affecting the pagefile then.  As that works as basically "on disk memory", and could slow down the system. 

Also, if using something like plex, if it's transcoding and storing the temp files on the C: drive.... that would also happen. 

Thank you for your assistance.

I am using XBMC. No transcoding. Just playing the mkv file on the client and the file is on the server. The server and client are connected via power line adapters. New HD is on the way and will let you know if that fixes it.

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