Home IBM, VMWare • Estimate Compression Rate on Storage Systems – IBM Comprestimator on ESX

Estimate Compression Rate on Storage Systems – IBM Comprestimator on ESX


The Comprestimator utility uses advanced mathematical and statistical algorithms to perform the sampling and analysis process in a very short and efficient way. The utility also displays its accuracy level by showing the maximum error range of the results achieved based on the formulas it uses. The utility runs on a host that has access to the devices that will be analyzed, and performs only read operations so it has no effect whatsoever on the data stored on the device. The following section provides useful information on installing Comprestimator on a host and using it to analyze devices on that host. Depending on the environment configuration, in many cases Comprestimator will be used on more than one host, in order to analyze additional data types.

It is important to understand block device behavior when analyzing traditional (fully-allocated) volumes. Traditional volumes that were created without initially zeroing the device may contain traces of old data in the block device level. Such data will not be accessible or viewable in the file system level. When using Comprestimator to analyze such volumes, the expected compression results will reflect the compression rate that will be achieved for all the data in the block device level, including the traces of old data. This simulates the volume mirroring process of the analyzed device into a compressed volume. Later, when volume mirroring is actually used to compress the data on the storage system, it will process all data on the device (including both active data and traces of old data) and get it compressed. After that when storing more active data on the compressed volume, traces of old data will start getting deleted by new data that is written into the volume. As more active data accumulates in the device the compression rate achieved will be adjusted to reflect the accurate savings achieved for the active data. This block device behavior is limited to traditional volumes and will not occur when analyzing thinly provisioned volumes.

Regardless of the type of block device being scanned, it is also important to understand a few characteristics of common file systems space management. When files are deleted from a file system, the space they occupied before being deleted will be freed and available to the file system even though the data on disk was not actually deleted but rather the file system index and pointers were updated to reflect this change. When using Comprestimator to analyze a block device used by a file system – all underlying data in the device will be analyzed, regardless of whether this data belongs to files that were already deleted from the file system. For example – you can fill a 100GB file system and make it 100% used, then delete all the files in the file system making it 0% used. When scanning the block device used for storing the file system in this example, Comprestimator (or any other utility for that matter) will access the data that belongs to the files that were already deleted.

In order to reduce the impact of block device and file system behavior mentioned above it is highly recommended to use Comprestimator to analyze volumes that contain as much active data as possible rather than volumes that are mostly empty of data. This increases accuracy level and reduces the risk of analyzing old data that is already deleted but may still have traces on the device.

Comprestimator version adds support for analyzing expected compression savings in accordance with XIV Gen3 storage systems running version 11.6, and Storwize V7000, SAN Volume Controller (SVC) and FlashSystem V9000 storage systems running software version 7.3. Among other enhancements in the software, version 7.3 adds support for the 2014 hardware models – Storwize V7000 Gen2, SVC DH8, FlashSystem V9000 AC1 and XIV Gen3.


  • Windows 2003 Server, Windows 2008 R2 Server, Windows 2012, Windows 7, Windows 8
  • Red Hat Enterprise Linux Version 5.x, 6.x, 7.1 (x86 64bit)
  • ESXi 4.1, 5.5, 6.0
  • Sun Solaris 10, 11
  • AIX 6.1, 7.1
  • HPUX 11.31
  • SUSE SLES 11 (x86 64bit)
  • Ubuntu 12 (x86 64bit)


  • Donwload and install the Software
  • Enable SSH on your ESX Server
  • Use an SFTP Tool (like WInSCP) to copy the file from the install path to the ESX Server

copy the file C:\Program Files(x86)\IBM\Comprestimator\ESX\comprestimator_esx to the folder ./tmp


  • change the file permission to allow the execution of the tool for the root User.


  • now you can connect with Putty to the ESX Server and list first the storage device you want to scan

run the following command

  • “esxcli corestorage device list | grep dev”


  • run the comprestimator on the LUNs you want to scan

” ./tmp/comprestimator_esx -s SVC -d devicepath ”

  • if you have many LUNs to scan you can automate the scan with using a config file and export the output in a csv file.

” ./tmp/comprestimator_esx -s SVC –config=file -c ./tmp/output ”

(Configuration file that contains list of devices to analyze. The file should contain a list of devices in the same format of the -d option, one device in each line)


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