Slow transfer speed due to SSD cache acceleration

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joshuacant
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Re: Slow transfer speed due to SSD cache acceleration

Post by joshuacant » Thu Sep 26, 2019 9:27 am

Thank you very much, AfroDieter. Great research done.

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SukkerFri
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Re: Slow transfer speed due to SSD cache acceleration

Post by SukkerFri » Thu Sep 26, 2019 4:03 pm

I've always put off the poor cache performance due to too cheap SSD's (Kingston A400). They were just laying around so I've been playing abit with Cache. But that just grinded my performance to a near hold.

I have a 2012 R2 connected via 10GBit to my NAS, so thats not the bottleneck. The RAID5 with 8TB HDDs (IronWolf) or the RAID5 with the 3TB HDDs (WD Red) are the clear bottlenecks. But adding SSD cache (Even read only with Samsung Pro, the performance gets worse than just the HDD's alone). Luckily when using iSCSI in 2012 R2, the RAM is used as cache and tasks can be quickly done, as long as there is free RAM :) Then, maybe for minuts, I can in Task Manager see RAM getting free'd up and the Disk(iSCSI) and ethernet adapter is going at it, but slowly. Like 10MByte/sek or something.

ATM I see QNAP SSD Cache as completely broken.
If you can't explain it simply, you dont understand it well enough
TS-1635 - 4GB RAM:
3x8TB IronWolf - Raid5
8x3TB WD Red - Raid5

sohouser1
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Re: Slow transfer speed due to SSD cache acceleration

Post by sohouser1 » Tue Oct 01, 2019 11:49 pm

Wow great work so far!

Just to confirm, I ran quite a few VM's using both qtier and SSD caching and very little sequential large file transfers. Even with random access VM's hitting the cache, it would still slow down when full. It was slow enough it corrupted 2 different VM's that I needed to restore from backup. (the OS got tired of waiting for I/O and timed out file access, not good with system files!)

joshuacant
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Re: Slow transfer speed due to SSD cache acceleration

Post by joshuacant » Sat Oct 05, 2019 5:37 am

Just wanted to report back that I let the SSD cache get up to 99% use, deleted it and re-added it, and the speeds never dropped below what I expected. Annoying, but not exactly a hardship to do once every few weeks. It'd be great if there were some command lines that could be run and a task scheduled to do it all every Sunday night at 3am, though.

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