SATA maximum cable length when connected via SAS controller and SFF cables

TrueNAS General
1

I understand that:

  1. The maximum recommended cable length for SATA is 1 meter, to ensure reliable data transfer without speed loss or signal integrity issues.
  2. The SAS standard supports cable lengths of up to 6 meters.
  3. SAS 2.0 is backward compatible with SATA drives.

Is this correct?

Now, let’s suppose the following setup with SATA drives:

LSI SAS 9212-4i4e card → 2m external SFF-8088 cable → Passive SFF-8088 to SFF-8087 converter → 0.5m internal SFF-8087 to 4x SATA cable → 4x SATA hard drives

Would this setup violate the SATA maximum recommended length of 1 meter? Because if I add up all the cables used, the total length is 2.5 meters…

2

I would have thought so.
This is one of the uses of a SAS Expander, instead of the Passive SFF-8088 to SFF-8087 converter

3

…plus the traces in the 8088-8087 adapter. Totally out of spec.
Shorter is better. Don’t even count on 1 m cables if you want reliable transfers.

4

That would be out of spec, this would be OK:

HBA > 2 meter cable > SAS expander > 1m cable to SATA disks

5

I see, then I’ll use a SAS expander.

Thank you all very much!