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There are a lot of explanations for the current Meltdown/Spectre crisis but many did not do a good job of explaining the core issue if how information is leaked from the secret side, to the attackers side. This is my attempt to explain it (mostly to myself to make sure I got it right). What […]
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As performance analysts we often have to summarize large amounts of data in order to make engineering decisions or understand existing behavior. This paper will help you do exactly that! Many analysts know that using statistics can help, but statistical analysis is a huge field in itself and has its own complexity. The article below […]
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We have started seeing misaligned partitions on Linux guests runnning certain HDFS distributions. How these partitions became mis-aligned is a bit of a mystery, because the only way I know how to do this on Linux is to create a partition using old DOS format like this (using -c=dos and -u=cylinders)
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Often we are presented with a vCenter screenshot, and an observation that there are “high latency spikes”. In the example, the response time is indeed quite high – around 80ms.
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Today I used fio to create some compressible data to test on my Nutanix nodes. I ended up using the following fio params to get what I wanted. buffer_compress_percentage=50 refill_buffers buffer_pattern=0xdeadbeef buffer_compress_percentage does what you’d expect and specifies how compressible the data is refill_buffers Is required to make the above compress percentage do what you’d […]
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A downtime classic, for several months in 2013 the troubles of a very particular website were front page news across the US. Full Story from Time Magazine (PDF) https://blog.newrelic.com/2014/03/26/depth-look-team-saved-healthcare-gov/
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When benchmarking filesystems or storage, we need to understand the caching effects. Most often this involves filling the cache and reaching steady state. But how long will it take to fill a cache of a given size? The answer depends of course on the size of the cache, the IO size and the IO rate. […]
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As an experiment, I wanted to (a) Create a HDD only container, and (b) measure the bandwidth I could achieve when backing up the SQL DB. This was performed on a standard hybrid platform with only 4 HDD’s in the node. First create a container, but add the special options “sequential-io-priority-order=DAS-SATA random-io-priority-order=DAS-SATA” which means that […]
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Recently I found that vdbench was not giving me the amount of outstanding IO that I had intended to configure by using the “threads=N” parameter. It turned out that with Linux, most of the filesystems (ext2, ext3 and ext4) do not support concurrent directIO, although they do support directIO. This was a bit of a […]
Published: (Updated: ) by . Leave a Comment on SATA on Nutanix. Some experimental data..
The question of why Nutanix uses SATA drive comes up sometimes, especially from customers who have experienced very poor performance using SATA on traditional arrays. I can understand this anxiety. In my time at NetApp we exclusively used SAS or FC-AL drives in performance test work. At the time there was a huge difference in performance between […]
Published: (Updated: ) by . Leave a Comment on Impact of Paravirtual SCSI driver VS LSI Emulation with Data..
TL;DR Comparison of Paravirtual SCSI Vs Emulated SCSI in with measurements. PVSCSI gives measurably better response times at high load. During a performance debugging session, I noticed that the response time on two of the SCSI devices was much higher than the others (Linux host under vmware ESX). The difference was unexpected since all the devices […]
Published: (Updated: ) by . 3 Comments on SuperScalin’: How I learned to stop worrying and love SQL Server on Nutanix..
TL;DR It’s pretty easy to get 1M SQL TPM running a TPC-C like workload on a single Nutanix node. Use 1 vDisk for Log files, and 6 vDisks for data files. SQL Server needs enough CPU and RAM to drive it. I used 16 vCPU’s and 64G of RAM. Running database servers on Nutanix is an […]
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One of the characteristics of a successful storage system for virtualized environments is that it must handle the IO blender. Put simply, when lots of regular looking workloads are virtualized and presented to the storage, their regularity is lost, and the resulting IO stream starts to look more and more random. This is very similar to […]
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If your underlying filesystem/devices have different response times (e.g. some devices are cached – or are on SSD) and others are on spinning disk, then the behavior of fio can be quite different depending on how the fio config file is specified. Typically there are two approaches 1) Have a single “job” that has multiple […]
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Many storage devices/filesystems treat blocks containing nothing but zeros in a special way, often short-circuiting reads from the back-end. This is normally a good thing but this behavior can cause odd results when benchmarking. This typically comes up when testing against storage using raw devices that have been thin provisioned. In this example, I have several […]
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I was speaking to one of our developers the other day, and he pointed me to the following paper: SEDA: An Architecture for Well-Conditioned, Scalable Internet Services as an example of the general philosophy behind the design of the Nutanix Distributed File System (NDFS). Although the paper uses examples of both a webserver and a gnutella client, […]