SAS 2308 optional RAID key

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takeawaydave

Member
Aug 20, 2013
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Hi - thanks Patrick for a really cool website - been checking it daily for a while now and thought might be time for a quick question tonight. Apologies if this has already been answered elsewhere on the forum.

I am thinking of purchasing an Supermicro X9SRH-7F and was reading the manual (as you do before buying) when I noticed the following relating to the SAS 2308 chip.

RAID Key Header (JRK1)
The RAID key header supports an optional RAID key (available separately). When plugged into this header, it will allow the user to enable the onboard SAS controller for software RAID 5 support (Intel or LSI).
No I have done a bit of reading around this RAID card and to be honest I am still feeling pretty clueless about RAID and gather that one way to use the SAS2308 is to "flash it to IT mode" - giving I guess enhanced functionality.

But whats the optional RAID Key ? I am thinking RAID 5 might be a handy basis for an array using Nexenta.
 

Jeggs101

Well-Known Member
Dec 29, 2010
1,529
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Hi - thanks Patrick for a really cool website - been checking it daily for a while now and thought might be time for a quick question tonight. Apologies if this has already been answered elsewhere on the forum.

I am thinking of purchasing an Supermicro X9SRH-7F and was reading the manual (as you do before buying) when I noticed the following relating to the SAS 2308 chip.



No I have done a bit of reading around this RAID card and to be honest I am still feeling pretty clueless about RAID and gather that one way to use the SAS2308 is to "flash it to IT mode" - giving I guess enhanced functionality.

But whats the optional RAID Key ? I am thinking RAID 5 might be a handy basis for an array using Nexenta.
If you do get the Supermicro X9SRH-7F you do NOT want the RAID key and RAID 5. You will use either RAID-Z or RAID-Z2 controlled by Nexenta and do not want the LSI controller to do anything other than present the disks to the OS.

Summary: Save money, don't get the optional RAID key.
 

takeawaydave

Member
Aug 20, 2013
62
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....You will use either RAID-Z or RAID-Z2 controlled by Nexenta and do not want the LSI controller to do anything other than present the disks to the OS...
Thanks Jeggs101 for the response. Please excuse my ignorance if it becomes apparent but isn't the idea of the SAS controller to have a HW raid system as opposed to a SW raid disk array setup ? The latter being what Nexenta would be providing and less preferable to a HW Raid.
 

mobilenvidia

Moderator
Sep 25, 2011
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New Zealand
Some OS's are best at doing RAID them selves in software.
ie ZFS is a self healing OS, when you add HW RAID the OS looses control of the integrity of the data.

Even with an OS where HW RAID is better, the SAS2308 is only good for simple RAID ie 0, 1 and 10
RAID 5 with no cache it will just be terrible at.
Use a proper MegaRAID controller for RAID 5/6

Take our word for it
 

takeawaydave

Member
Aug 20, 2013
62
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Use a proper MegaRAID controller for RAID 5/6
I assume you are referring to a dedicated PCI based controller card ? Any recommendations ?

I am starting to think perhaps go for a plain board with a SATA controller and expand later on via a controller card.
 

Biren78

Active Member
Jan 16, 2013
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Thanks Jeggs101 for the response. Please excuse my ignorance if it becomes apparent but isn't the idea of the SAS controller to have a HW raid system as opposed to a SW raid disk array setup ? The latter being what Nexenta would be providing and less preferable to a HW Raid.
There are two types of SAS controllers, those that are HBA's (sas 2300 and what you want with Nexenta) and those with RAID. Here are two to read from this site on the topic:
http://www.servethehome.com/difference-hardware-raid-hbas-software-raid/
http://www.servethehome.com/anatomy-hardware-raid-controller/