# Cluster

# Is it possible to migrate volumes to another location?

cioctl migrate is used to move a volume from one Storidge cluster to another Storidge cluster.

cioctl migrate docker migrates docker named volumes, while cioctl migrate generic supports specifying the mountpoint for the data to be migrated. See cioctl migrate (opens new window) docs for details.

# What about split brain? Do you need three managers minimum like Swarm?

Certain nodes have a manager/leader function. For Storidge, the leader is the sds node. This represents the control plane through which commands go to for processing. There are two other backup controller nodes to ensure there is no single point failure for the control plane.

# Mounting cloud service provider block storage is already one mount. On node failure, isn't remounting the block storage on a new node adding more latency?

Mounting and unmounting cloud block storage takes a long time and is sometimes not consistent or reliable. That's why the Storidge software leaves the cloud block storage mounted on instances, and creates a shared storage pool/abstraction layer from the mounted block storage.

Virtual volumes for containers are created from the storage pool. The virtual volumes are seen as local Linux block devices which are formatted with the filesystem of choice. This enables the Storidge volumes to be quickly and reliably mounted/unmounted on demand, as the scheduler restarts apps on different nodes. This abstraction layer shields applications from the limitations of the underlying cloud infrastructure.

For more info on the abstraction layer, read the How It Works blog (opens new window)

# How does updates for Storidge cluster work? Currently rebooting all my cluster instances for patches means tons of downtime.

Storidge supports cluster aware updates. Cluster aware updating upgrade nodes to the latest software releases, while the cluster is online and services continue to run.

If an update is available, the node is cordoned, services drained to other nodes, update software is downloaded and installed. When the software installation is completed, the node is rebooted and automatically rejoins the cluster.

See cioctl node update (opens new window) info for details.

# Why does Storidge do data collection during cluster initialization?

On physical servers with flash memory devices (e.g. SSD or NVME drives), the Storidge software runs a data collection process as part of cluster initialization. This is about a 30 minute process to gather performance data on the cluster. The end result is an IOPS and bandwidth budget that is used by the QoS capability to allocate performance on demand to individual volumes.

As performance limits are assigned to applications, the Storidge software will adjust the IOPS and bandwidth budget. If there is insufficient performance available to support guaranteed performance for all apps, you will get an event notification.

# If I create a single node cluster do I still run cioctl init <token> command?

For single node cluster, run cioctl create to start a cluster, then run the cioctl init <token> command to initialize the cluster for use. When initialization completes, you can login and start running apps.

You can also run the cioctl create --single-node command to create a single node cluster. This will automatically create a cluster and initialize it. When initialization completes, just login and begin running apps.

# How is total capacity, used capacity, free capacity and provisioned capacity calculated?

The cio info command returns information about total, used, free and provisioned capacity in the cluster.

Total capacity is the raw capacity of all drives in the storage pool, minus space allocated for metadata. Storidge reserves 1GiB per drive for metadata. Using a 5 node cluster with three 100GiB drives per node as an example:

5 nodes x 3 100GiB = 1500GiB - (1GiB x 15 drives) = 1485GiB total capacity in storage pool

Used capacity is capacity that is allocated to both thin and thick provisioned volumes, plus capacity that is pre-allocated to each node. When data requests are received, the pre-allocated capacity are assigned to thin provisioned volumes so I/O requests can be completed immediately. This eliminates the latency of issuing a request across the network to another node to get volume capacity allocated.

For example, with a 100GiB, 2 copy thick provisioned volume:

100GiB x 2 copy = 200GiB used by volumes

5 nodes x 50 allocation units x 16MiB = 4GiB pre-allocated capacity

200GiB + 4GiB = 204GiB used capacity

Free capacity is total capacity in storage pool minus the used capacity, i.e.

Total capacity - Used capacity = Free capacity

Provisioned capacity is the specified capacity for all volumes (thin or thick provisioned) and includes capacity used for data redundancy. Since volumes can be thin provisioned, the provisioned capacity can be much larger than physical capacity actually in the cluster, i.e. capacity can be overprovisioned.

Example with one 100GB, 2 copy thin provisioned volume and one 100GB, 3 copy thin provisioned volume:

(1 volume x 100GiB x 2 copy) + (1 volume x 100GiB x 3 copy) = 500GiB provisioned capacity

Allocated % is the percentage number of allocation units assigned to a volume. Thick provisioned volumes are always 100% allocated. For example a 1GiB, 2 copy thick provisioned volume will have 128 allocation units:

1GiB x 2 copy = 2GiB / 16MiB = 128 allocation units

A 1GiB, 2 copy thin provisioned volume with 8 allocation units (128MiB) is:

8 / 128 x 100 = 6.3% allocated

# Can I reboot a cluster with a missing or failed node?

Storidge supports booting a cluster with one missing or failed node. After the cluster is reformed, the missing or failed node will show status 'maintenance'.

The Storidge software allows 30 minutes for a maintenance node to be restored. If the maintenance node is not recovered and rejoined to the cluster within 30 minutes, it will be automatically removed so rebuild of data that was on the maintenance node can proceed.

# Can I extend the maintenance window from 30 minutes?

Yes, you can increase the time for maintenance from the default 30 minutes. Use the cioctl node show-time command to see the remaining time left for maintenance.

To extend time, use the cioctl node extend-time command. For example, to increase maintenance time by 15 minutes, run:

cioctl node extend-time 15

# How do I mitigate network congestion issues on a cluster?

Symptoms of network congestion are dropped network packets, missing heartbeats, failed nodes, lost network connections, etc.

Network congestion is more likely to happen when cloud instances are provisioned with just one network interface. If the use case supports workloads with high data throughput, this can interrupt internode cluster traffic and break a cluster.

Suggestions to address this issue include:

  1. Monitoring bandwidth usage for each instance to confirm if network bandwidth is being exhausted. Entries in syslog that indicate nodes added to failed list, ISCSI connection issues, or missing heartbeats are also indicators of network congestion.

  2. If there is only one network interface per instance, it will be supporting incoming data streams, orchestrator system internode traffic and Storidge data traffic.

For use cases handling a lot of front end data, consider splitting off the storage traffic to a separate network, e.g. use instances with two network interfaces. Assign an interface for front-end network traffic and assign second interface for storage network.

When creating the Storidge cluster, you can specify which network interface to use with the --ip flag, e.g. run cioctl create --ip When you run the cioctl node join command on the storage nodes, it will suggest an IP address from the same subnet.

  1. Verify if incoming data is going to just one node. Consider approaches such as a load balancer to spread incoming data across multiple nodes.

  2. Calculate the amount of network bandwidth that will be generated by your use case. Verify that the network interface is capable of sustaining the data throughput. For example, a 10GigE interface can sustain about 700MB/s.

  3. In calculations for data throughput, note that for every 100MB/s of incoming data, there is a multiple of the throughput used for replicating data. For 2-copy volumes, 100MB/s will be written to local node and 100MB/s will go through the network interface to other nodes as replicated data, i.e. 100MB/s incoming data stream results in 200MB/s of used network bandwidth.

# How do I check if my virtual server or cloud instance is supported?

The Storidge software currently recognizes the virtual servers and cloud instances below:

System Product Name Virtual Server/Cloud Instance
Bochs Qemu (emulated)
Droplet Digital Ocean
Product Name: HVM domU Xen
KVM Virtual Machine Qemu with KVM
Manufacturer: Microsoft Corporation Microsoft VirtualPC (Hyper-V)
OpenStack Nova OpenStack Nova
VirtualBox VirtualBox
VMware Virtual Platform VMware

Run dmidecode -s system-product-name to confirm if your instance is on the list. If not on the list, support can be quickly added. Please pass request to support@storidge.com.

Last Updated: 7/27/2020, 2:38:26 AM