Hello everyone,
I am planning to switch my existing QNAP setup to TrueNAS because I want to connect a bit more storage and gain more flexibility and overall compute power. The new solution should also be energy efficient, especially in idle mode, given the high energy prices in Germany.
I have drafted a detailed plan for a low-power NAS server and would appreciate feedback from the community on whether this plan is technically feasible and if anyone has experience regarding power consumption.
For the CPU, I am relying on the Intel 1700 platform from the consumer sector, as it is very energy efficient when idling. This comes with the drawback that there are not many PCIe lanes available.
Therefore, the LSI 9500-i8 HBA will be used in a PCI slot. A SAS Expander will be added to connect enough drives.
Requirements:
- HDDs: 12x 3.5" HDDs (approx. 150 MB/s each)
- SSDs: 4x 2.5" SSDs (approx. 500 MB/s each)
- NVMe Option 1 (9500-i8): 1x NVMe SSD (directly connected to the HBA)
- NVMe Option 2 (9500-i16): 3x NVMe SSDs (directly connected to the HBA)
My Planned Setup:
HBA and SAS Expander
HBA: Broadcom LSI SAS 9500-i8 (in PCIe4.0 x8 Slot)
- PCIe4.0 x8 Slot: high bandwidth
- Tri-Mode support for NVMe
- very low idle consumption 6-7W (thanks to ARM architecture)
SAS Expander Adaptec AEC-82885T
- enough ports
- 12GBits/s SAS-3 interface
- idle power consumption???
Cabling/Connection Scheme (Based on 9500-i8)
HBA 9500-i8
- HBA Port 1 (mini SAS HD, 4x 12GBit/s Lanes = 4.8GB/s): → Goes to a SAS Expander
- SAS Expander Port1 (1.2GB/s)
- HDD1 (150MB/s), HDD2 (150MB/s), HDD3 (150MB/s), SSD1 (500MB/s) = (950MB/s)
- SAS Expander Port2 (1.2GB/s)
- HDD4, HDD5, HDD6, SSD2 (950MB/s)
- SAS Expander Port3 (1.2GB/s)
- HDD7, HD82, HDD9, SSD3 (950MB/s)
- SAS Expander Port4 (1.2GB/s)
- HDD10, HDD11, HDD12, SSD4 (950MB/s)
- SAS Expander Port1 (1.2GB/s)
- HBA Port 2 (mini SAS HD, 4x 12GBit/s Lanes = 4.8GB/s): → Goes to an NVMe SSD
- Mini SAS HD to NVMe Adapter
- NVMe SSD PCIe x4 (1.5MB/s)
- Mini SAS HD to NVMe Adapter
Feasibility Check & Bandwidth
1. Does the connectivity work?
To connect the 16 drives to just one port, I need the SAS Expander. I watched the video about the Adaptec AEC-82885T on “Art of Server” (Let’s settle this question about the AEC-82885T SAS expander), which confirms that it should work that way.
Question to the community:
Do you see any issues here in the interaction between TrueNAS and the LSI 9500-i8 (in IT mode) in connection with the AEC-82885T?
2. Is the bandwidth sufficient?
The connection between the HBA and the Expander uses 4 SAS lanes (12 Gb/s per lane).
- Total Bandwidth (SAS3): 4 x 1.2GB/s per Lane approx 4.8 GB/s
-
- Total Requirement: 3800MB/s (or 3.8GB/s)
- 12 HDDs x 150MB/s = 1800MB/s
- 4 SSD x 500MB/s = 2000MB/s
- Total Requirement: 3800MB/s (or 3.8GB/s)
-
Question to the community:
The available bandwidth of approx. 4.8 GB/s should easily cover the maximum total requirement of approx. 3.8 GB/s for all 16 drives.
The Crucial Question: Idle Power Consumption of the Expander
The most critical component for my low-power build is the Adaptec AEC-82885T SAS Expander. Every additional 10W costs me 32EUR annually, which quickly adds up.
I have read that the maximum power consumption can be up to 25W. The datasheet mentions an operating current of 1.34A at 12 VDC, which corresponds to a maximum power consumption of approx. 16.08 W.
Since the expander will spend most of its time in idle, this value is critical for me. I could not find any reliable information on the idle power consumption anywhere. The expander is based on the Broadcom SAS35x36 chip, which is said to be based on an ARM architecture and supports various power-saving modes.
My Main Question:
What is the real idle power consumption of the Adaptec AEC-82885T SAS Expander when operating with 16 connected, but mostly spun-down, drives?
Every real measurement or experience is gold!
