One of the important characteristics of flash memory is wear. We know from previous articles in this series that flash packages consist of dies, which contain planes, which contain blocks, which in turn contain pages. We also know that these pages contain individual cells which store the bits of data… but to understand what wear is we need to look a little bit closer at those cells, where we will find something called (more...)
If you’ve been unfortunate enough to follow my dithering on Twitter recently you’ll know that I’ve been lurching between thinking that there is and isn’t a problem with Oracle’s tracking of I/O statistics in its AWR reports.
I’m now convinced there is a problem, but I can’t work out what causes it… so step 1 is to describe the problem here, after which step 2 will probably be to sit back and hope someone far (more...)
I’ve posted a new installation cookbook for using Oracle within a virtual machine running on Oracle VM. Surprisingly, I was unable to come up with a satisfactory method of accessing external storage that did not involve the use of Oracle ASMLib…
Filed under: Blog, Cookbooks, Database, Flash, Linux, Storage Tagged: cookbooks, database, oracle, oracle vm
I’ve spent a lot of time in this blog series talking about the challenges involved in using flash, such as the way that pages have to be erased before they are written and the restriction that erase operations take place on a whole block. I also described the problem of erase operations being slow in comparison to reads and writes – and the resulting processes we have to put in place to manage that problem (i. (more...)
I was recently contacted by a customer who runs a busy ERP system on their Oracle database. Their users have been screaming for some time about unpredictable performance, where application screens which would usually open in under a second suddenly take an age. ERP systems are legendary for this, of course, because as each screen loads the application tends to fire off a glut of queries to populate all the various fields, graphs and so (more...)
For the last couple of posts in this series I’ve been banging on about the importance of garbage collection (GC) in a flash system. I attempted to show you what happens if you don’t perform any GC at all (clue: you turn your flash device into a slow ROM), but clearly in the real world every flash array or SSD vendor has GC technology built into their flash translation layer. So why am I going (more...)
Follow the link to find out whether I thought it was the most amazing product in the history of storage, or simply a rehashed Pillar Axiom hybrid array with some SSDs and a ton of marketing.
In the last post in this series I discussed some of the various tasks that need to be performed by the flash translation layer – the layer of abstraction that sits between us and the raw NAND flash on which we desire to store our data. One of those tasks is the infamous garbage collection process (or “GC”) – and in these next couple of posts I’m going to look into GC a little deeper.
A couple of posts ago in this series, I explained how a NAND flash die is comprised of planes, which contain blocks, which contain pages… which contain individual cells of data. Read operations take place at the page level, as do write operations (although we call them program operations in the flash world). But crucially, erase operations take place at the block level and so affect multiple pages.
Erases are also (more...)
I am aware that (more...)
The effect of ASM redundancy/parity on read/write IOPS – SLOB test case! for Exadata and non-Exa environments
Last week I had a lengthy post at oracle-l that tackles Calibrate IO, Short Stroking, Stripe size, UEK kernel, and ASM redundancy effect on IOPS Exadata which you can read here
followed by interesting exchange of tweets with Kevin Closson here (see 06/21-22 tweets) which I was replying in between games at UnderwaterHockey US Nationals 2012 which we won the championship for the B division I have my awesome photo with the medal here
This post will detail on the ASM redundancy/parity effect on IOPS… if… by changing the ASM redundancy (external, normal, and high) will it decrease the workload (more...)
I have received a fair number of responses to my previous post on this subject (some via comments and some via email). I thought the discussion worthwhile enough to punch it up a bit more here.
As I pointed out in the previous post, EMC can easily match NetApp's play to back up ExaData with the following:
As Geoff Rosser so correctly pointed out, this answer is incomplete. Yes, Data Domain is an awesome Oracle backup solution. Yes, it provides incredible deduplication rates for Oracle database environments. (Thanks, dynamox.) However, it is not the only viable solution from (more...)
On my post about observing the Exadata V1 I had an interesting comment posted by Mark Seger (author of collectl and collectl utilities) about the correlation of activities across a system, the sample and snap time, and seeing the state of the subsystem before and after…
The comment made me curious about the effect of snap intervals on the performance numbers of the datafiles and block devices.. especially on the latency numbers.. so I made a few test cases and created some scripts that would give me 5 seconds, 10 minutes, and 60 minutes output of (more...)