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multipath I/O loadbalance
if i have only one host connect to one EMC CX, and only one LUN is assigned to this host.
there is four paths configured for this LUN, with 2 is in the owner SP. ALUA mode is not used.
when the host write to this LUN, how many pathes will be used to issue I/O. one or two?
dynamox
2 Intern
2 Intern
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20.4K Posts
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December 22nd, 2010 19:00
zone 1 - hba1 - SPA0
zone 2 - hba1 - SPB0
zone 3 - hba2 - SPA1
zone 4 - hba2 - SPB1
if current LUN owner is SPA, you have licensed PowerPath ..the host will use hba1 and hba2 to write to LUN using SPA0 and SPA1 concurrently.
dingding1
125 Posts
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December 23rd, 2010 21:00
if the I/O from two path to the owner SP are out of order, who will reassemble them?
SAS, FC are all serial protocol, they are all fast than parallel SCSI, so when multiple path is used simultaneously, maybe it will be slower than using only a single path?
it seems multipath software is only useful when load on host is very high, for example, VMware ESX.
Conor
341 Posts
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January 4th, 2011 03:00
if the I/O from two path to the owner SP are out of order, who will reassemble them?
>> If both the paths to the owning SP die for whatever reason, PowerPath sends a trespass message to the array to transfer the LUN ownership to the standby SP. PowerPath then marks both (previously active) paths as dead and resumes IO on the paths to the new SP.
PowerPath really does come into it's own in high IO environments, it is only then that you see the real benefits of load-balancing, and the performance increases they bring. This does not only have to be ESX environments, any server that runs IO-intensive applications will see similar benefits.