Added blog for System requirements

Author: mcoonen

_posts/2024-08-15-optimize-iiif-performance.md

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+---
+layout: post
+read_time: true
+show_date: true
+title: Power up! Optimize IIIF user experience
+description: Configuration settings for a well performant IIIF user experience with Omeka S 
+date: 2024-08-15
+img: posts/power-up-web.jpg
+tags: [ omeka s, iiif ]
+author: Maarten Coonen
+---
+
+Running Omeka S with the IIIF modules configured on a machine with average hardware leads to a workable situation in most cases. 
+However, there are some things you need to know in order to make your user's experience much better. 
+
+
+## Boost image processing performance with vips
+Image files are being preprocessed (resized and tiled) by Omeka S at time of upload so that the IIIF ImageServer can 
+optimally serve the tiles whenever an image is requested over HTTP. Omeka S has support for multiple image processing
+libraries that are available as PHP extensions. In most cases, GD or ImageMagick are being used, as these are preinstalled by 
+most Linux distributions. The [ImageServer module](https://omeka.org/s/modules/ImageServer/) recommends to use the 
+[**vips** image processor](https://www.libvips.org/), as this one is much faster.
+
+Our benchmarks confirm that vips is blazingly fast. Processing a 127 MB TIF file during upload on our test Omeka S system
+took 15 minutes with Imagemagick and only 1 second with vips! With the JPEG 2000 format the difference is even more extreme:
+44 minutes with Imagemagick vs. 1 second with vips.
+As one can imagine, these reductions in processing time greatly enhance the productivity of collection managers working
+with the system. 
+
+vips is easy to install. Just use the command below to install it from your distro's package manager if you have 
+Debian 12 (or higher) or Ubuntu 24.04 (or higher). People running Ubuntu 20.04 can follow the installation instructions
+from our [previous blog](./installing-iiif-with-omekas.html).
+```bash
+# Debian 12 & Ubuntu 24.04
+apt-get install libvips-tools
+```
+
+## Choose "Tiled tiff" as tiling method
+The image preprocessing (resizing and tiling) jobs in Omeka S ensure that (high-resolution) image files are converted 
+to a format that can be optimally served over the internet, while still preserving all details and zoomability. One way
+to do this is by using a pyramidal image format like [pyramidal TIFF](https://training.iiif.io/iiif-online-workshop/day-two/fileformats.html).
+
+![pyramidal tiff](assets/img/posts/pyramidal-format.png)
+A pyramidal image consists of multiple layers, each representing the image in different resolution. At initial load, 
+the layer with the lowest resolution (and smallest size) is served to the image viewer. When a user zooms in, a deeper layer
+with higher resolution is used to serve only the tiles that are in the viewpane. The rest of the image is not loaded, which
+saves network bandwidth and results in a faster loading time.
+
+Source image files that are being uploaded to Omeka S are stored in the `original/` sub folders. The tiled copies are
+stored in the `tile/` sub folders.
+```bash
+./files/original/<itemID>/<filename>.jpg  ------|
+                                                |
+./files/original/<itemID>/<filename>.jp2  ------|---- Pyramidal TIFF ----> ./files/tile/<itemID>/<filename>.tif
+                                                |
+./files/original/<itemID>/<filename>.tif  ------|
+```
+
+The Omeka S module [ImageServer](https://omeka.org/s/modules/ImageServer/) provides multiple tiling methods:
+- Deep Zoom Image
+- Zoomify
+- Jpeg 2000
+- Tiled tiff
+
+Based on our tests, the **Tiled tiff** method works best, as it saves disk storage capacity, has the fastest upload experience
+and has a reasonable page loading time. 
+
+Note: although the "Deep Zoom Image" and "Zoomify" options serve images the fastest, they are still not our preferred format
+as they cause HTTP-404 errors for tiles that cannot be loaded. 
+
+
+## Increase page load performance with parallel processing
+The time of single core processors has passed a long time ago. Nowadays, all CPUs have 2 or more cores that can do work 
+simultaneously. Apache, PHP-FPM and Omeka S are able to work multi-threaded, thereby putting multiple cores to work in
+serving the image tiles to the user requesting it. This greatly enhances performance. 
+
+Modern data centers run virtualized servers and allow you to increase the amount of CPU cores with the click of a
+button, as long as you continue to pay your bills. Virtualized cores cost money as well!
+
+We've conducted a series of tests with various source file types (JP2000, TIFF, JPG compression quality 80 (JPGq80) and
+JPG compression quality 40 (JPGq40)) to determine the optimal amount of CPU cores. Our base line tests were run on 4 CPU
+cores. Subsequently, we've repeated the same tests with 8 and 16 cores.
+
+The results are shown in the figure below. On average, 8 CPU cores load a page 31.3% (8 cores) and 36.5% faster 
+(16 cores) compared to 4 cores when tested with these file types. We expect that adding more cores will increase performance
+even further, although the gain per added core will be less.
+![]("assets/img/posts/testing-cpu-cores.png)
+
+
+## TODO: Save disk space and increase page load performance by using JPG compressed source images
+tiled tiff from jp2 processed again by vips at page load. WE don't see this with other formats. This is why jp2 performs least.
+TIFF format loads fastest, but takes a lot of disk space.
+JPGq80 is the best compromise
+
+
+## Conclusion
+Our preferred setup consists of a machine with the characteristics below.
+
+- CPU: 16 cores or more
+- Memory: 16 GB or more
+- Disk: 250 GB or more
+- Operating System: Ubuntu 20.04 or higher
+- Web server: Apache 2.4 or higher with HTTP/2 and PHP-FPM modules and CORS headers enabled (see details in [previous blog](./installing-iiif-with-omekas.html))
+- PHP: version 8.2 or higher
+- Image processing: vips 8.14.1 or higher & Imagemagick 6.9.11 (with jp2 extension enabled) or higher
+- Omeka S module Image server - Image processor: Automatic (Vips when possible, ... (etc.))
+- Omeka S module Image server - tiling type: Tiled tiff