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Can SAS expander topology contain loops?

maxtch
By maxtch
in Servers, NAS, and Home Lab
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What I mean is, for a system with two SAS expanders, while each one of them have a link to the SAS RAID card, there is also a cross-link between the two. Can I do this?

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Posted
5 hours ago, maxtch said:

What I mean is, for a system with two SAS expanders, while each one of them have a link to the SAS RAID card, there is also a cross-link between the two. Can I do this?

Umm.. why would you do that?

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On 2/26/2021 at 4:56 PM, Nick7 said:

Umm.. why would you do that?

Redundancy and load balancing.

The Fruit Pie: Core i7-9700K ~ 2x Team Force Vulkan 16GB DDR4-3200 ~ Gigabyte Z390 UD ~ XFX RX 480 Reference 8GB ~ WD Black NVMe 1TB ~ WD Black 2TB ~ macOS Monterey amd64

The Warship: Core i7-10700K ~ 2x G.Skill 16GB DDR4-3200 ~ Asus ROG Strix Z490-G Gaming Wi-Fi ~ PNY RTX 3060 12GB LHR ~ Samsung PM981 1.92TB ~ Windows 11 Education amd64
The ThreadStripper: 2x Xeon E5-2696v2 ~ 8x Kingston KVR 16GB DDR3-1600 Registered ECC ~ Asus Z9PE-D16 ~ Sapphire RX 480 Reference 8GB ~ WD Black NVMe 1TB ~ Ubuntu Linux 20.04 amd64

The Question Mark? Core i9-11900K ~ 2x Corsair Vengence 16GB DDR4-3000 @ DDR4-2933 ~ MSI Z590-A Pro ~ Sapphire Nitro RX 580 8GB ~ Samsung PM981A 960GB ~ Windows 11 Education amd64
Home server: Xeon E3-1231v3 ~ 2x Samsung 8GB DDR3-1600 Unbuffered ECC ~ Asus P9D-M ~ nVidia Tesla K20X 6GB ~ Broadcom MegaRAID 9271-8iCC ~ Gigabyte 480GB SATA SSD ~ 8x Mixed HDD 2TB ~ 16x Mixed HDD 3TB ~ Proxmox VE amd64

Laptop 1: Dell Latitude 3500 ~ Core i7-8565U ~ NVS 130 ~ 2x Samsung 16GB DDR4-2400 SO-DIMM ~ Samsung 960 Pro 512GB ~ Samsung 850 Evo 1TB ~ Windows 11 Education amd64
Laptop 2: Apple MacBookPro9.2 ~ Core i5-3210M ~ 2x Samsung 8GB DDR3L-1600 SO-DIMM ~ Intel SSD 520 Series 480GB ~ macOS Catalina amd64

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Posted

A proper enterprise level DAS using SAS drives would do this internally. SAS supports multiple links, so what effectively happens is every drive is connected to both controllers, and then the two controllers are connected back to the host.

 

I wouldnt think simply plugging two SAS expanders together would work though.

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6 hours ago, maxtch said:

Redundancy and load balancing.

I don't understand what you'd gain this way?
You still have single point of failure - SAS RAID card.

 

SAS drive support 2 paths.

Proper way is either to have 2 SAS RAID cars which support HA, or use two cards in IT mode and let host handle multipathing.

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i just googled this to find some info and it seems like this is not supported with SAS Expanders like this.

 

But i also found that when you google SAS Expander loop your profile pic now shows up on the first page of the images 😄

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