San block sizes

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San block sizes

leehbi

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February 22, 2018 at 9:51 am

#333700

I appreciate this isn't a SAN forum. I'm exploring recommended block sizes to have for an all SSD SAN for SQL DW workload. I'm learning that bigger block sizes can massively impact SAN performance. Is it as straightforward as going for 32KB / 64KB or is there other trade offs to consider for SQL Server?

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Eirikur Eiriksson SSC Guru Points: 182915 More actions · Answer 1

leehbi - Thursday, February 22, 2018 9:51 AM
I appreciate this isn't a SAN forum. I'm exploring recommended block sizes to have for an all SSD SAN for SQL DW workload. I'm learning that bigger block sizes can massively impact SAN performance. Is it as straightforward as going for 32KB / 64KB or is there other trade offs to consider for SQL Server?

You would want the data reads to be aligned to 64kb which is the read size of the SQL Server, for log files specs, look into Kalen Delaney work on the SQL Server Internals, I normally go for 32Kb on the SSD's for the logs.
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Are you seeing any performance problems? Does the server have multiple NICs/LUNs?

leehbi SSCrazy Points: 2874 More actions · Answer 2

We're seeing a ceiling on reads of around 700MB/s kind of expect 1200MB/s+ with 64KB blocks. We have fibrechannel connections to the network. These aren't being filled so I think we're looking at the SAN at the minute.

ZZartin SSC-Dedicated Points: 30921 More actions · Answer 3

leehbi - Friday, February 23, 2018 9:10 AM
We're seeing a ceiling on reads of around 700MB/s kind of expect 1200MB/s+ with 64KB blocks. We have fibrechannel connections to the network. These aren't being filled so I think we're looking at the SAN at the minute.

Are you comparing the speed under load from SQL server to the theoretical max speed in a pure data push scenario? Those aren't necessarily going to be equal.

leehbi SSCrazy Points: 2874 More actions · Answer 4

I have stats from San provider for the 1200MB - I appreciate these are based on 100% random access and are theoretical, even so I expect more than 700MB.

Enterprise DBA SSC-Addicted Points: 478 More actions · Answer 5

Leehbi,

Designed and configured properly you will be limited by HBA’s and/or limits placed on the storage frame. Storage can handle much more than one host. Two dual port HBA’s with all 4 ports enabled should get you closer to 3 GB/sec.