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February 24th, 2012 14:00
H800 and use of x4 wide ports
My understanding is the cable between an H800 and an MD1200 is actually a x4 SFF-8808 connector that carries 4 PHYs, or (4) 6Gbit SAS connections.
My question is are all of these PHYs used when talking to the SAS expander in the MD1200? There is no doc on the MD1200 controller that I can find. Does the H800 try to use all 4 SAS ports on the cable and will the MD1200 controller allow simultaneous connections on all 4 to 4 different disks?
This is pertinent to how many disks will saturate an H800 connection, and total throughput.
Thanks!
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avhays
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March 1st, 2012 17:00
Well, no one responded but this is what I think may be correct. Please respond if it isn't.
- Dell H810 is probably based on the LSI 2208 chip (no published specs yet), as opposed to the H800 based on the 2108 chip. Probably double the throughput.
- As far as comparison to an iSCSI box (MD or EqualLogics) in terms of speed only:
Bandwidth to drives:
2 x 10Gbit iSCSI box has 2.5Gbyte bandwidth pipe to drives assuming both 10Gbit links can be used simultaneously by an initiator.
8 port x 6Gbit SAS H-810 has 4.8Gbyte (assuming 8b/10b SAS encoding) bandwidth pipe to drives using both x4 (wide) cables and boxes with two EMM's (MD1200, MD1220) whose SAS expanders will use both ports A and B on a SAS disk. Expanders for H710 implementations evidently do not use redundant wide links and is limited to half- 2.4Gbyte. Of course the max number of internal drives usually on an H710 is not large enough to saturate 2.4Gbyte.
Load balancing:
iSCSI such as EqualLogics has three ways to do this using both 10Gbit links and moving data around on RAID sets. No iSCSI box has RAID 60.
H810 balances across all 8 SAS ports and implements RAID 60 which means data can be striped across many drives and ports. This will effectively result in load balancing.
Caching most used data:
Both iSCSI EqualLogics and H810 (FastPath, Cachecade) can use SSD.