Should SANs be patched to fix the Spectre and Meltdown bugs? Er ... yes and no | 1/12/2018 | Staff
bluelilly (Posted by) Level 3
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Analysis Is the performance sapping spectre of the X86 Spectre/Meltdown bug fixes hanging over SAN storage arrays? The general assumption is "yes" but five suppliers say not.

You would expect SANs to need patching; they run their controller software on X86 servers after all.

UK - Storage - Architect - Chris - Evans

UK storage architect Chris Evans writes: “Patching against Meltdown has resulted in performance degradation and increased resource usage, as reported for public cloud-based workloads.”

His understanding is that “the overhead for I/O is due to the context switching that occurs reading and writing data from an external device. I/O gets processed by the O/S kernel and the extra work involved in isolating kernel memory introduces an extra burden on each I/O. I expect both traditional (SAS/SATA) and NVMe drives would be affected because all of these protocols are managed by the kernel.”

Difference - SAS/SATA - NVMe - NVMe

He said he does wonder whether there’s a difference between SAS/SATA and NVMe, simply because NVMe is more efficient.

Specifically, for traditional storage arrays: “The additional work being performed with the KAISER patch appears to be introducing extra CPU load in the feedback reported so far. This means it also must affect latency. … The impact to traditional storage is two-fold. First, there’s extra system load, second potentially higher latency for application I/O."

Customers - Patch - Need - Array - CPU

Customers implementing this patch need to know if the increased array CPU levels will have an impact on their systems. A very busy array could have serious problems.

"The second issue of latency is more concerning. That’s because like most performance-related problems, quantifying the impact is really hard. Mixed workload profiles that exist on today’s shared arrays mean that predicting the impact of code change is hard. Hopefully, storage vendors are going to be up-front here and provide customers with some benchmark figures before they apply any patches.“

Nothing - Carry

Nothing to see here - carry on...

But five suppliers say no,...
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