Cluster Operation

How do I know that the new replication parameters have been successfully applied to the cluster?

To check whether the replication process is complete, run the pstorage top command, press the V key on your keyboard, and check information in the Chunks field:

• When decreasing the replication parameters, no chunks in the overcommitted or deleting state should be present in the output.
• When increasing the replication parameters, no chunks in the blocked or urgent state should be present in the output. Besides, the overall cluster health should equal 100%.

For details, see Monitoring the Status of Replication Parameters .

How do I shut down a cluster?

To shut down a Parallels Cloud Storage cluster:

1. Stop all clients.
2. Stop all MDS servers.
3. Stop all chunk servers.

For details, see Shutting Down Parallels Cloud Storage Clusters .

What tool do I use to monitor the status and health of a cluster?

You can monitor the status and health of your cluster using the pstorage top command. For details, see Monitoring Parallels Cloud Storage Clusters .

To view the total amount of disk space occupied by all user data in the cluster, run the pstorage top command, press the V key on your keyboard, and look for the FS field in the output. The FS field shows how much disk space is used by all user data in the cluster and in how many files these data are stored. For details, see Understanding Disk Space Usage .

How do I configure a Parallels Cloud Server server for a cluster?

To prepare a server with Parallels Cloud Server for work in a cluster, you simply tell the server to store its Containers and virtual machines in the cluster rather than on its local disk. For details, see Configuring virtual machines and Containers .

Why vmstat/top and pstorage stat show different IO times?

The pstorage and vmstat / top utilities use different methods to compute the percentage of CPU time spent waiting for disk IO ( wa% in top , wa in vmstat , and IOWAIT in pstorage ). The vmstat and top utilities mark an idle CPU as waiting only if an outstanding IO request is started on that CPU, while the pstorage utility marks all idle CPUs as waiting, regardless of the number of IO requests waiting for IO. As a result, pstorage can report much higher IO values. For example, on a system with 4 CPUs and one thread doing IO, pstorage will report over 90% IOWAIT time, while vmstat and top will show no more than 25% IO time.

What effect tier numbering has on Parallels Cloud Storage operation?

When assigning storage to tiers, have in mind that a tier number in itself does not have any effect on drive performance. However, the general recommendation is to assign faster storage drives to lower tiers.

This recommendation is related to how Parallels Cloud Storage works with storage space. If a storage tier runs out of free space, Parallels Cloud Storage will attempt to temporarily use a lower tier, and if those are full too, a higher tier. If you add more storage to the original tier later, the data, temporarily stored elsewhere, will be moved to the original tier where it should have been stored originally.

For example, if you try to write data to the tier 2 and it is full, Parallels Cloud Storage will attempt to write that data to tier 1, then to tier 0, and then to tier 3. If you add more storage to tier 2 later, the aforementioned data, now stored on the tier 1, or 0, or 3, will be moved back to the tier 2 where it was meant to be stored originally.