Administrator’s Command Line Guide

Chapter 6. Maximizing Cluster Performance
6.2 Checking Data Flushing
Before creating the cluster, you are recommended to check that all storage devices (hard disk drives, solid
disk drives, RAIDs, etc.) you plan to include in your cluster can successfully flush data to disk when the server
power goes off unexpectedly. Doing so will help you detect possible problems with devices that may lose data
stored in their cache in the event of a power failure.
Acronis Storage ships a special tool, vstorage-hwflush-check, for checking how a storage device flushes data to disk
in an emergency case such as power outage. The tool is implemented as a client/server utility:
• Client. The client continuously writes blocks of data to the storage device. When a data block is written,
the client increases a special counter and sends it to the server that keeps it.
• Server. The server keeps track of the incoming counters from the client so that it always knows the
counter number the client will send next. If the server receives the counter that is less than the one
already stored on the server (e.g., because the power was turned off and the storage device did not flush
the cached data to disk), the server reports an error.
To check that a storage device can successfully flush data to disk when the power fails, follow the procedure
below:
On the server part:
1. On a Acronis Storage server other than the one with the storage device to check, install the vstorage-hwflush-
check tool. This tool is part of the vstorage-ctl package and can be installed with this command:
# yum install vstorage-ctl
2. Run the vstorage-hwflush-check server:
# vstorage-hwflush-check -l
On the client part:
1. On the Acronis Storage server with the storage device you want to check, install the vstorage-hwflush-check
tool:
# yum install vstorage-ctl
2. Run the vstorage-hwflush-check client, for example:
# vstorage-hwflush-check -s vstorage1.example.com -d /vstorage/stor1-ssd/test -t 50
where
64