Large Sequential Read

Large sequential read is one of the common data access patterns. For instance, the Decision Support System (DSS) workload or Business Intelligence (BI) system relies heavily on this data pattern to extract useful information timely and generate reports by scanning and analyzing multi-terabyte databases.

With the arrival of Big Data, this data pattern is likely to become more important. And Big Data would likely require storage systems to optimize the performance of large sequential reads.

On NetApp Fabric-Attached Storage (FAS) systems, there is a tuning you can do to enhance large sequential read performance. TR-3760 recommended to tune the setting of one nonstandard flag:

setflag wafl_max_write_alloc_blocks 256

The default value of the flag is 64. You may wonder why tuning this flag would have anything to do with large sequential read performance. The fact of matter is that good sequential read performance starts with good, contiguous data layout on disk. TR-3760 pointed it out correctly:  “this flag optimized the WAFL® on-disk data layout.”

Of course, it goes without saying that Big Data also requires Big Pipe. As the 10GbE (FCoE or iSCSI) now becoming mainstream; and 40GbE and even 100GbE on the horizon, the pipe is definitely getting bigger and bigger.

Thanks for reading.

 

Comments

[Maddenca]

Beginning in 8.0.1 there is a per volume option to set the same:

ntap01> vol options vol2 max_write_alloc_blocks 256

[Wei Liu]

It's great to be able to do this on per volume basis. However, I'm not seeing this option. I'm running ONTAP v8.0.1 7-mode. Could you tell me how to access this option?

Thanks,
Wei

[Wei Liu]

Sorry, I looked more carefully and now I see the max_write_alloc_blocks under the volume option. Good to go. -Wei