Preclear


gooner_47

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Just checking on the current status of preclear. I've seen plenty of threads about it but some quite old and mentioning gfjardim has to fix up the plugin before it can be used. 

 

What's the situation at the moment, am I safe to use the plugin with the latest version of unraid, or should I just use a script? If so, which one is best and are there step by step instructions for how to do this?

 

Many thanks, Luke

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The current version (2018.10.7) is compatible with the current Unraid (6.6.5). I've run it on three disks (not simultaneously) recently, without any problems. I had given up on it when it started spamming the syslog and I was using badblocks to test disks instead but when the author started maintaining it again I decided to give it another chance and currently it works just fine. I don't like the statistics reporting part but at least that's optional.

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16 hours ago, tronyx said:

Do you still need to download the script(s) in order for it to work or are they finally bundled?

There's a fast script written by the plugin's author included in the package. It's all self-contained and currently it works well. I've used it on a number of disks since Unraid 6.6.5 was released - just one at a time, in my case.

 

The older scripts can be used instead but they need patching, which is a nuisance. Unless you particularly need an old script you might as well use the built-in one.

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There was a dark period when the plugin wasn't being maintained. I guess the author was too busy - it happens. Unraid was moving ahead and using newer sources and the plugin just became a liability. It hooks into the code for the Main page of the GUI and interacts with the Unassigned Devices plugin and caused the UD author a lot of headaches. It also spammed the syslog so a lot of people who had previously used it uninstalled it and looked for alternatives. Then suddenly the author reappeared, fixed it up and it's currently better than it's ever been.

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I installed it last night, used the included script on a fresh install of unraid and it's currently pre-clearing 3 drives which are at the zeroing stage. 

 

Perhaps an interesting data point: This is on an old testbed running an AMD Athlon X2 6000+ with 8GB ram. I started the one preclear and waiting to see the read speeds. They were around ~180MB/s on a WD Red 4TB. After about 10 minutes I fired up the second. Immediately I noticed the CPU fan kick up a fair bit. I flipped over to the dashboard and noticed pretty much 100% CPU usage. To think, that used to be a flagship CPU... 

 

Anyway, I have 4 drives total but the last one hasn't been shucked yet so I fired up the third (8TB X300) and let it be. 

 

The two WD Reds stayed around the 175MB/s mark. The Toshiba started off around 225MB/s and this morning is still going around 210MB/s. 

 

The two WD Reds are currently zeroing at 180MB/s. So all in all, while the CPU is still pegged (I have a household fan going on the whole open setup) it - and the preclear plugin - are handling the task admirably. 

 

Oh, and last night someone had suggested I use more than 1GB of ram in the system. As this is just a backup system to fire up once a month or so, I thought it would be a great place to use my 256MB*4 chips. After that suggestion, I maxed out the board at 8GB, thinking more overhead is certainly not a bad idea. When the process first started, it was using 24% of the memory. This morning it's up to 29%. After seeing this, I'm leaning more towards using my 4*512MB sticks when I finish the build - just in case I use this system for future pre-clears. 

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Have a look at the output of htop. I think you'll find the CPU is actually spending most of its time stuck in threads that are waiting for disk I/O rather than actually working hard crunching numbers.

 

Preclear uses a lot of RAM.

 

The Athlon 64 X2 6000+ was a fine processor in its day - considerably better than the Pentium 4 and Pentium D competition - though it wasn't used as much as it deserved because Intel paid the big system builders not to use AMD products. I think the flagship was actually the Athlon 64 X2 6400+ Black Edition (90nm, Windsor), though. I still have mine.

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