[Tig] 1Tb & 2Tb Raid disks, what make/model?

Jean-Francois Panisset panisset at gmail.com
Tue Mar 8 19:26:04 GMT 2011


>> Something to consider is getting drives "nearline drives with a SAS
>> interface", sometimes called "fat sas" drives: the advantage is that
>> you don't have to add "interposer" dongles to the drives to get dual
>> porting, so that's one less piece of electronics that can break. It is
>> also said that since the SAS protocol is more efficient than the SATA
>> protocol, you can get a bit more performance from the same mechanicals
>> with a SAS interface than with a SATA interface.
>
> Is this instead of a SAS expander? are these SATA drives with an interface?

These drives share the same mechanical "innards" as SATA drives, but
they have a SAS interface. From what I've been told, the advantages
are:

http://en.wikipedia.org/wiki/Serial_attached_SCSI#Nearline_SAS

- The SAS protocol is more robust and allows for greater overlap of
operations / less involvement from the host controller, even when you
enable NTQ on SATA drives: so the "same" drive will perform better
with a SAS interface than SATA. Also, in the specific case of Seagate
enterprise drives, the SAS version is 6 gbit/sec, the SATA version is
3 gbit/sec.
- In a dual controller RAID / dual interface JBOD enclosure, you need
a so called interposer dongle to allow a SATA drive to be visible from
both controllers / interfaces: typically, this interposer card goes at
the back of the drive between the drive connector and the backplane
connector. So although the SAS drive may be a bit more expensive, some
of that cost is offset by the fact that you don't need interposer
cards, and that also lowers the number of components in the system.
- What specific model of JBOD are you planning to hook up to the R380
controller? Presumably, this is a JBOD enclosure with one or two SAS
interface controllers: these would connect to the R380 controller with
something like a SFF-8088 external mini-SAS connector which supports 4
SAS "channels": the interface card in the enclosure is responsible for
mapping the slots in the enclosure to SAS channels, thus acting as a
SAS expander.

In the past, I've used a dual interface Promise JBOD connected to a
3ware RAID controller with 2 x miniSAS cables, that worked fine.

JF



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