SAS Expander, parity check, rebuilding an array

[volume]

Hello

 

I would like some help to understand what SAS expander speed should i need, for my specific needs for a cold storage server storing media files, without vm's. Unfortunatly the link here didn't help me http://www.sasexpanders.com/faq/

 

In the case of a cold storage server with 15-24 drives of 8ΤB-10TB,

will we gain parity/rebuilding speed if we use a 12G SAS Expander instead of 6G or 3G?

 

What are the most crucial factors, that makes parity check or rebuilding an array, faster?

The ram and cpu is crucial or its only a matter of hard drives speeds?
 

thanks

Edited February 7, 2019 by volume

[JorgeB]

With a SAS2 expander (and SATA3/SAS2 devices) you'll get up to 4400MB/s using dual link, so with 24 drives, up to 183MB/s, so it can bottleneck a little if you're using fast modern drives that can get up to 250/275MB/s on the outer sectors, though it's still pretty good.

 

With an LSI SAS3 HBA + expander you'll get up to around 6000MB/s, the PCIe slot will be the limit.

 

As for the hardware, for single parity a Sandybridge or newer dual core CPU is enough, for dual parity a high clock Skylake/Kabylake would be the best, for RAM use the max speed for that CPU in dual channel.

[volume]

58 minutes ago, johnnie.black said:

With a SAS2 expander (and SATA3/SAS2 devices) you'll get up to 4400MB/s using dual link, so with 24 drives, up to 183MB/s, so it can bottleneck a little if you're using fast modern drives that can get up to 250/275MB/s on the outer sectors, though it's still pretty good.

  

With an LSI SAS3 HBA + expander you'll get up to around 6000MB/s, the PCIe slot will be the limit.

 

As for the hardware, for single parity a Sandybridge or newer dual core CPU is enough, for dual parity a high clock Skylake/Kabylake would be the best, for RAM use the max speed for that CPU in dual channel.

 

My current drives are Seagate ironwolf 8TB and Seagate archive 8TB.

Just to make my decision a little bit clear.

 

Lets say that i have a tower case able to host 24 drives, and i also have a motherboard, cpu, ram and psu.

What else do i need to connect the 24 drives? An HBA card and a SAS expander?

 

Could you please give me a very rough estimate of cost for a 12Gb SAS Expander and 6Gb SAS Expander?

thanks

Edited February 7, 2019 by volume

[JorgeB]

7 minutes ago, volume said:

An HBA card and a SAS expander?

Yes.

 

Good SAS2 expanders, for example the Intel 24 and 32 ports models, can be found on ebay starting at around $75, though you'll need the 32 port one for max bandwidth with 24 disks.

 

SAS3 expanders are f*ing expensive, I was looking for one myself and didn't find any below around $300.