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If I am buying some used servers with 24-25x SAS that I hope to someday upgrade from 6Gb/s to 12Gb/s RAID, do I need to be concerned at all with the backplane that the drives are plugging into not being able to handle the higher speeds?

Looking at the HP DL180 G6 servers.

Alan
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1 Answers1

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It depends on what you're doing...

The HP ProLiant DL180 G6 is an end-of-lifed server. It's way out of production. You don't have any options to upgrade this hardware to 12Gbps. It will be stuck at 6Gbps with a 24+1 port expander fed to two 4-lane 6Gbps SFF-8087 ports. I'm assuming you'll be using an HP Smart Array P410 controller... Most of the drives in that model are on one SAS port, so assume 4 x 6Gbps == 24Gbps throughput to the controller.

SAS link speeds matter, and then they don't... If you're using SSDs, the situation is different than spinning SAS disks. The latter are probably capable of 1 to 1.5Gbps speeds, so 24 x 1.5 == 36Gbps. The disk backplane is oversubscribed... and that's fine.

Note: If you use SATA drives, the link speed will only be 3Gbps per disk in that server.

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ewwhite
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  • Thanks, trying to get an education on maximizing performance without just throwing money into a $15K server. I finally dropped off the media server at the datacenter Friday, I am putting together another one that will be for the database / apache server. Have considered a FusionIO card for this one or other PCIe SSD cards but you get pretty limited storage that way. – Alan Jan 25 '15 at 21:53
  • I should mention we are wanting to put together a site similar to jsfiddle. This will be more than raw bandwidth, and more about seek times but just trying to figure out what I don't know about SAS / RAID hardware, which is about everything :) – Alan Jan 25 '15 at 21:59
  • @Alan Throughput on an oversubscribed backplane has an upper-limit as the number of disks increase. IOPS will scale with disk count until you hit the controller's limit (*20,000 IOPS*). – ewwhite Jan 25 '15 at 22:09
  • Does that mean I was an idiot to get 4 SSD drives with 90k IOPS and put them into a RAID on this system? – Alan Jan 25 '15 at 22:41
  • Unfortunately you don't get very much benefit from those. :( – Citizen Jan 25 '15 at 22:43
  • It isn't too late for me to grab a new raid controller if that is a deal breaker on performance, should I grab an LSI MegaRaid card to put in there? – Alan Jan 25 '15 at 22:44
  • @Alan It depends on which *specific* SSDs you purchased. If they are SATA SSDs, you'll be [capped at 300Mbps per disk](http://serverfault.com/questions/531499/3rd-party-ssd-drive-in-hp-proliant-server-only-shows-3g-transfer-speed). In a worst-case scenario, they may not behave with the controller. You could use an LSI controller in the server, although you lose the HP management functions. Be sure to buy an "8i" controller with TWO SAS SFF-8087 ports. – ewwhite Jan 25 '15 at 23:08