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What can SAS do
SAS is a pretty new technology. Reading about it, I find myself asking several questions that I cannot find answers to.
Maybe here's the right place.
I understand each SAS drive has 2 ports. Using 2 expanders (connected also to each other), it can be connected to 2 SAS HBAs (or 2 SAS HBA ports) on the same system. This type of setup creates a full-mesh multipath. On Linux, a similar FC setup will expose the disk (its WWNN) multiple times to the OS (#times == #target-ports x #hba ports). Is that what's happening with a full-mesh SAS fabric?
Some HBA vendors mention "multipath", but I fail to understand what they are talking about. Do they present to the OS a single device (e.g. based on its WWNN), and handle the multipathing resolution in the HBA ? in the low-level driver? or using some additional software?
Are there any problems with such SAS full-mesh fabrics?
Thanks,
Dan
Discussion started by dbbd , on 20 October 09:37 AM
Replies
storageio,
Tuesday, October 20, 2009
Dan,
Are you looking to a) build out a SAS mesh with SAS switches and individual drives in enclosures (e.g. JBOD) attached to a SAS PCIe RAID or basic adapter card, or, b) attaching SAS RAID arrays (e.g. those with single or dual controllers) to a single or multiple servers via SAS, or, c) basicly understand how SAS addressing, logical and physical connectivity takes place?
In general, similar to Fibre Channel (FC), a SAS device such as a dual controller RAID array can be attached to mutliple HBAs on the same or different servers. Thus, multipathing software/drivers can be used and are avialbel for SAS for path management similar to on FC.
Here's are some links for the SAS/SCSI industry trade group site along with some of their tutorials and other SAS related material.
http://www.scsita.org/aboutscsi/sas/STA_6G_SAS.pdf
http://www.scsita.org/aboutscsi/sas/tutorials/SAS_General_overview_public.pdf
http://www.scsita.org/aboutscsi/sas/tutorials/SAS_FCP_comparison_public.pdf
http://www.scsita.org/aboutscsi/sas/SAS_IG.pdf
Here's a document that shows some of the things seen from a SAS adapter. Note that while this is an HP example, you can find similar SAS material for adapters, switches, drive/JBOD enclosures as well as SAS RAID arrays at Adaptec, Dell, DotHill, IBM, LSI, Promise and Sun among others.
http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c01475627/c01475627.pdf
hope this helps
Cheers gs
Are you looking to a) build out a SAS mesh with SAS switches and individual drives in enclosures (e.g. JBOD) attached to a SAS PCIe RAID or basic adapter card, or, b) attaching SAS RAID arrays (e.g. those with single or dual controllers) to a single or multiple servers via SAS, or, c) basicly understand how SAS addressing, logical and physical connectivity takes place?
In general, similar to Fibre Channel (FC), a SAS device such as a dual controller RAID array can be attached to mutliple HBAs on the same or different servers. Thus, multipathing software/drivers can be used and are avialbel for SAS for path management similar to on FC.
Here's are some links for the SAS/SCSI industry trade group site along with some of their tutorials and other SAS related material.
http://www.scsita.org/aboutscsi/sas/STA_6G_SAS.pdf
http://www.scsita.org/aboutscsi/sas/tutorials/SAS_General_overview_public.pdf
http://www.scsita.org/aboutscsi/sas/tutorials/SAS_FCP_comparison_public.pdf
http://www.scsita.org/aboutscsi/sas/SAS_IG.pdf
Here's a document that shows some of the things seen from a SAS adapter. Note that while this is an HP example, you can find similar SAS material for adapters, switches, drive/JBOD enclosures as well as SAS RAID arrays at Adaptec, Dell, DotHill, IBM, LSI, Promise and Sun among others.
http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c01475627/c01475627.pdf
hope this helps
Cheers gs
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