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ScanMaximumConcurrent - Concurrent Scanning


I have set ScanMaximumConcurrent to "4" for my setup.  Is there any drawbacks to this setting?  Too high, too low?


My server has an LSI 9211-8i HBA connected to an LSI Expander hot-swap SAS2 blackplane (the Supermicro SC846 chassis for those wondering).


The Expander utilizes all 4x 6 Gbps channels to have a total of 24 Gbps, or about 3,000 MB/s (megaBytes per seconds).  Since each HGST 4GB HDD I have can only substain about 130 MB/s, I was thinking "4 concurrent" at ~520 MB/s isn't an issue since that's only ~17% of the overall bus.  Or, the same speed as my Sata 6 SSD I have in the pool on the same controller.


The only drawback I can see is bandwidth.  But please correct me if I am wrong.


I'm down to about 14 HDDs in this chassis in the pool.  So, having only 1 scan at a time on the SAS2 bus was taking days to get through.


I'd like to bump it to 8x if there isn't any issue?


But, not all drives gets the same bandwidth.  For example, here are the four running right now:


108 MB/s

83 MB/s

71 MB/s

133 MB/s


Should I not be running this many concurrent?  Can I go higher?   :)

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You should definitely be able to go higher. :)


As for drawbacks, power consumption, heat generation, vibration.  Maybe performance issues, if you're able to bottleneck the hardware.


Aside from that, there shouldn't be any drawbacks.

And I'm assuming you've disabled the throttling option to not interfere with activity on the same controller.




I have a similar setup. Specifically an IBM ServeRAID M1015 cross flashed (so basically the same controller as the one you listed), an intel SAS Expander card, and in a Norco RPC-4220 (which I got from a friend, for a steal!) 


I've set the value to "0" on my system, and it's fun watching it scan *all* of the disks in the system at the same time.  And that's 17 disks attached to the one expander right now.



As for bottlenecks,  you've listed that the HGST drives generally don't get more than 130MB/s sustained.  For the one cable, that should allow you to scan about 20 drives. (specifically, 23.0769...).  After that, you'll start bottlenecking.   But I suspect that isn't an issue for your system. 


(the card itself should be able to support ~30 drives at 130MB/s) 




As for the disparity in speed, that depends on a number of factors.  Where it is in the disk, how active the system is, if the specific disk is doing something already, how many remapped sectors the disk has (as these may cause the read heads to jump around), etc.   

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Perfect, that's what I was looking for!


Ah, so setting it to 0 is unlimited.  Done and done!  Yep, I already disabled the throttling on the same controller.


A glance over at the watt meter with all 14 HDDs scanning (8x HGTS 4GB, 3x Seagate Blue 4GB, and various other WD Green drives) shows 188 Watts at the wall.  So, power consumption: check.


The hottest drive is 37C, with most around 27 - 32C.  The chassis fans are spinning at 50% PWM.  Heat generation: low, check.


Vibration.. Eh...  That's actually one of the reasons I switched to HGST with their marketing advertisement for vibration isolation... If it's a gimmick or not, we'll see.


With all HDDs spun down it idles around 85 Watts...  The LSI Expander uses 12 Watts and the LSI card (as well as the IBM M1015) uses 9 Watts.  One day I'll have 8x HDDs large enough that I won't need the LSI HBA nor Expander, saving another 21 Watts.


I too have 2x IBM M1015s cross-flashed to the 9211-81 (posted in another thread about them recently).  I moved to the LSI 9211-8i as it was better for cable routing in my chassis.  


I need to sale them... They are just sitting in a box next to me.   :)  Humm, no "Forsale" section here at Stablebit?

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Yes, 0 is "unlimited" or "unrestricted".  You can find this setting and others here:


This talks about how to set them and what they do. Some are self explanatory, but others ... not so much.


And I was looking for the image earlier, and just found it.  I apologize for the overly large image size for this... 





As for the max speeds, another thing to check is with the datasheet.  I know the Archive drives indicate 190MB/s as the max speeds, and I believe that different lines of drives do have different max speeds.  So that will also affect this.



As for the vibration stuff, WD claims the same about the Red (and especially the Red Pro) drives. 




As for power consumption, I couldn't compare, as I've never really looked into it (have solar, so haven't needed to)


And yeah, more drives at once definitely allow for faster scans in the work window. :)

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