Announcing qdda 2.0

It’s almost a year since I blogged about qdda (the Quick & Dirty Dedupe Analyzer).

qdda is a tool that lets you scan any Linux disk or file (or multiple disks) and predicts potential thin, dedupe and compression savings if you would move that disk/file to an All Flash array like DellEMC XtremIO or VMAX All-flash. In contrast to similar (usually vendor-based) tools, qdda can run completely independent. It does NOT require a registration or sending a binary dataset back to the mothership (which would be a security risk). Anyone can inspect the source code and run it so there are no hidden secrets.

It’s based upon the most widely deployed database engine, SQLite, and uses MD5 hashing and LZ4 compression to produce data reduction estimates.

The reason it took a while to follow-up is because I spent a lot of evening hours to almost completely rewrite the tool. A summary of changes:

• Run completely as non-privileged user (i.e. ‘nobody’) to make it safe to run on production systems
• Increased the hash to 60 bits so it scales to at least 80 Terabyte without compromising accuracy
• Decreased the database space consumption by 50%
• Multithreading so there are separate readers, workers and a single database updater which allows qdda to use multiple CPU cores
• Many other huge performance improvements (qdda has demonstrated to scan data at about 7GB/s on a fast server, bottleneck was IO and theoretically could handle double that bandwidth before maxing out on database updates)
• Very detailed embedded man page (manual). The qdda executable itself can show its own man page (on Linux with ‘man’ installed)
• Improved standard reports and detailed reports with compression and dedupe histograms
• Option to define your own custom array definitions
• Removed system dependencies (SQLite, LZ4, and other libraries) to allow qdda to run at almost any Linux system and can be downloaded as a single executable (no more requirements to install RPM packages)
• Many other small improvements and additions
• Completely moved to github – where you can also download the binary

Read the overview and animated demo on the project homepage here: https://github.com/outrunnl/qdda

HTML version of the detailed manual page: https://github.com/outrunnl/qdda/blob/master/doc/qdda.md

As qdda is licensed under GPL it offers no guarantee on anything. My recommendation is to use it for learning purposes or do a first what-if analysis, and if you’re interested in data reduction numbers from the vendor, then ask them for a formal analysis using their own tools. That said, I did a few comparison tests and the data reduction numbers were within 1% of the results from vendor-supported tools. The manpage has a section on accuracy explaining the differences.

Baking a cake: trading CPU for IO?

Sometimes I hear people claim that by using faster storage, you can save on database licenses. True or false?

The idea is that many database servers are suffering from IO wait – which actually means that the processors are waiting for data to be transferred to or from storage – and in the meantime, no useful work can be done. Given the expensive licenses that are needed for running commercial database software, usually licensed per CPU core, this then leads to loss of efficiency.

Let’s see if we can visualise the problem here with a common world example – Baking a cake.
 
 

Oracle ASM vs ZFS on XtremIO

Background

In my previous post on ZFS I showed how ZFS causes fragmentation for Oracle database files. At the end I promised (sort of) to also come back on topic around how this affects database performance. In the meantime I have been busy with many other things, but ZFS issues still sneak up on me frequently. Eventually, I was forced to take another look at this because of two separate customers asking for ZFS comparisons agaisnt ASM at the same time.

The account team for one of the two customers asked if I could perform some testing on their lab environment to show the performance difference between Oracle on ASM and on ZFS. As things happen in this business, things were already rolling before I could influence the prerequisites and the suggested test method. Promises were already made to the customer and I was asked to produce results yesterday.

Without knowledge on the lab environment, customer requirements or even details on the test environment they had set up. Typical day at the office.

In addition to that, ZFS requires a supported host OS – so Linux is out of the question (the status on kernel ZFS for Linux is still a bit unclear and certainly it would not be supported with Oracle). I had been using FreeBSD in my post on fragmentation – because that was my platform of choice at that point (my Solaris skills are, at best, rusty). Of course Oracle on FreeBSD is a no-go so back then, I used NFS to run the database on Linux and ZFS on BSD. Which implicitly solves some of the potential issues whilst creating some new ones, but alas.

Solaris x86

This time the idea was to run Oracle on Solaris (x86) that had both ZFS and ASM configured. How to perform a reasonable comparison that also shows the different behavior was unclear and when asking that question to the account team, the conference call line stayed surprisingly silent. All that they indicated up front is that the test tool on Oracle should be SLOB.

Getting the Best Oracle performance on XtremIO

(Blog repost from Virtual Storage Zone – Thanks to @cincystorage)

UPDATE: I’ll say it again because there seems to be some confusion: THIS IS A REPOST!

Original content is from the Virtual Storage Zone blog (not mine). Just reposted here because it’s interesting and related to Oracle, performance and EMC storage. Enjoy…

XtremIO is EMC’s all-flash scale out storage array designed to delivery the full performance of flash. The array is designed for 4k random I/O, low latency, inline data reduction, and even distribution of data blocks.  This even distribution of data blocks leads to maximum performance and minimal flash wear.  You can find all sorts of information on the architecture of the array, but I haven’t seen much talking about archive maximum performance from an Oracle database on XtremIO.

The nature of XtremIO ensures that’s any Oracle workload (OLTP, DSS, or Hybrid) will have high performance and low latency, however we can maximize performance with some configuration options.  Most of what I’ll be talking about is around RAC and ASM on Redhat Linux 6.x in a Fiber Channel Storage Area Network.

Read the full blogpost here.

 

The public transport company needs new buses

A public transport company in a city called Galactic City, needs to replace its aging city buses with new ones. It asks three bus vendors what they have to offer and if they can do a live test to see if their claims about performance and efficiency holds up.

The transport company uses the city buses to move people between different locations in the city. The average trip distance is about 2 km. The vendors all prepare their buses for the test. The buses are the latest and greatest, with the most efficient and powerful engines and state of the art technology.

Getting the most out of your server resources

As an advocate on database virtualization, I often challenge customers to consider if they are using their resources in an optimal way.

And so I usually claim, often in front of a skeptical audience, that physically deployed servers hardly ever reach an average utilization of more than 20 per cent (thereby wasting over 80% of the expensive database licenses, maintenance and options).

Magic is really only the utilization of the entire spectrum of the senses. Humans have cut themselves off from their senses. Now they see only a tiny portion of the visible spectrum, hear only the loudest of sounds, their sense of smell is shockingly poor and they can only distinguish the sweetest and sourest of tastes.

– Michael Scott, The Alchemyst

About one in three times, someone in the audience objects and says that they achieve much better utilization than my stake-in-the-ground 20 percent number, and so use it as a reason (valid or not) for not having to virtualize their databases, for example, with VMware.

Linux Disk Alignment Reloaded

My all-time high post with the most pageviews is the one on Linux disk alignment: How to set disk alignment in Linux. In that post I showed an easy method on how to set and check disk alignment under linux.

ZFS and Database fragmentation

Disk Fragmentation – O&O technologies.
Hope they don’t mind the free advertising

Yet another customer was asking me for advice on implementing the ZFS file system on EMC storage systems. Recently I did some hands-on testing with ZFS as Oracle database file store so that I could get an opinion on the matter.

One of the frequent discussions comes up is on the fragmentation issue. ZFS uses a copy-on-write allocation mechanism which basically means, every time you write to a block on disk (whether this is a newly allocated block, or, very important, overwriting a previously allocated one) ZFS will buffer the data and write it out on a completely new location on disk. In other words, it will never overwrite data in place. Now a lot of discussions can be found in the blogosphere and on forums debating whether this is really the case, how serious this is, what the impact is on performance and what ZFS has done to either prevent, or, alternatively, to mitigate the issue (i.e. by using caching, smart disk allocation algorithms, etc).

In this post I attempt to prove how database files on ZFS file systems get fragmented on disk quickly. I will not make any comments on how this affects performance (I’ll save that for a future post). I also deliberately ignore ZFS caching and other optimizing features – the only thing I want to show right now is how much fragmentation is caused on physical disk by using ZFS for Oracle data files. Note that this is a deep technical and lengthy article so you might want to skip all the details and jump right to the conclusion at the bottom :-)

Managing REDO log performance

I have written before about managing database performance issues, and the topic is hot and alive as ever. Even with today’s fast processors, huge memory sizes and enormous bandwidth to storage and networks.

warning: Rated TG (Technical Guidance required) for sales guys and managers ;-)

A few recent conversations with customers showed other examples of miscommunication between IT teams, resulting in problems not being solved efficiently and quickly.
In this case, the problem was around Oracle REDO log sync times and some customers had a whole bunch of questions to me on what EMC’s best practices are, how they enhance or replace Oracle’s best practices, and in general how they should configure REDO logs in the first place to get best performance. The whole challenge is complicated by the fact that more and more organizations are using EMC’s FAST-VP for automated tiering and performance balancing of their applications and some of the questions were around how FAST-VP improves (or messes up) REDO log performance.

Performance – The database stack

As mentioned before, I frequently find myself in discussions around Oracle performance and how an Oracle database behaves on EMC storage. It turns out that often there is a lot of confusion on how the different layers interact with each other and very few people seem to understand the whole stack.

So I started a personal challenge to make a “one picture tells more than 1000 words” complete overview of the Oracle on EMC database stack.

I failed.

Turns out it’s nearly impossible to get everything in one picture without cutting corners.

So here is a simplified (and therefore incorrect) picture. It ignores certain complexities and is far from complete, and might even contain errors.