Slow parity speed and array writes (no more than 25mb/s)


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Sorry, new to Unraid. I've searched the forums for solutions, tried a few things here and there but remain troubled by slow read/write speeds (25mb/s each way) to my array. Parity build is also limited to 25mb/s. Basically I can't get more than around 25mb/s read/write speeds total. A file copy to the array will basically halve the write speed (at the time of this screenshot, a file is being copied to the Unraid array). Reads don't seem to be affected.  I'm running 6.10.rc, with Twonkyserver (as a music server) and one Win10 VM active (as a Chia node). 




This wasn't the case when my array was first put together, consisting of 1 parity and 3 data 10TB drives driven all by my motherboard's SATA ports. I was getting between 100-200mb/s read and writes to and from the array (its much faster on the Cache drive, up to 900mb/s on my 10g network) then. However, when I added 8 more drives (1 added parity drive and 7 data drives, all 10TB too) from my old QNAP NAS and expanded my array, I started to get the slow speeds. The 8 added drives run off a 12-port Asmedia SATA expander card.  


Right now, I'm beginning to think that there is something wrong on the hardware side but I was wondering if I missed anything in the configuration of my array. My diagnostics file is attached. Any advice is appreciated!

Edited by Starrus
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  • Starrus changed the title to Slow parity speed and array writes (no more than 25mb/s)

Thanks again.


I hope so. This is the second time I'm syncing from scratch. The first time I aborted on the third day. I'm basing the estimate based off the Array Operation section of the main page. The speed has doubled now that the file copy into the array is done. 


Are these sync speeds expected of Unraid for a 12-drive array (2 parity, 10 data)?   



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I thought that was the problem, after all the troubleshooting that I did. One of which was a Diskspeed benchmark, that shows higher burst speeds for drives connected to the motherboard. Those on the ASmedia were at 100+ mb/s sustained, that that was only benchmarked one drive at a time. 




I'm going to order a used LSI HBA and see how that improves the speeds. Thanks again.

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4 minutes ago, Starrus said:

I'm going to order a used LSI HBA and see how that improves the speeds. Thanks again.


Be careful and vet the vendor carefully as you are 'buying' the vendor and not the board.  Try to buy from a vendor in your country as you will have more options for resolution if the product is not as represented.  (Buying LSI boards is a bit of a minefield as LSI no longer exists as a separate corporation.   Buying 'new' boards is a real issue as there are manufacturers making counterfeit older model boards with the LSI logo.)

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1 hour ago, Starrus said:

Thanks for the heads up... Unfortunately, there's always a risk with buying online.


There are a couple of vendors on e-bay who are based in the USA that have provided hundreds of used boards (apparently, from retired server farms) and have good reputations.  They also update many of the boards to the latest IT-Mode software.  These boards do cost a bit more...


LSI is now a part of Broadcom and they are still selling the older LSI chip sets to people who want to buy them.  (Broadcom is supplying actual boards that use the latest chip sets  and you can find them on their website.)   Manufacturer(s) in China have copied the old LSI boards (down to the paper labels in some cases) and are selling them as new LSI boards.  I call these 'counterfeit' as the names of the these manufacturers are not provided.   The quality of the remaining components required are unknown and those buying one is a bit of a gamble.   So if you buy one, the vendor who sells it to you is your only point of contact for remedy if you have an issue.

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Thanks @JorgeB! Just to close the loop, it was my 8-port Asmedia 1166 card that was bottlenecking read/write speeds. I managed to get my hands on an old HP H240 HBA and performance has gone up significantly! Its more what I expect from these enterprise-grade drives. 




@Frank1940It was a good thing that the person I got the HBA card from was reliable. So far so good. The card runs hot but that's a known issue. Only issue was with one of the 8087 cables that he passed to me, where one channel was faulty. He told me about it and I took them as they were what was available on hand. Will be ordering new ones soon (and add back my 10th data drive).   


Once again, thanks everyone. 



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9 minutes ago, Starrus said:

(and add back my 10th data drive

Keep in mind that when you add a data drive to an array with valid parity, the drive will be irretrievably wiped and formatted before it is added. If there is any data you wish to keep on that drive, you can do a new config and rebuild parity with the data on the added drive intact.


Unless you really need the extra capacity, it would be prudent to keep the drive aside as a spare, so when a drive fails you will have a ready replacement.


Also, it's really, really handy to have a spare slot physically open for future heavy maintenance if needed. Much easier to keep a slot open than juggle things to make one available in a pinch.

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