Documentation

# Expand a Distributed MinIO Deployment

A distributed MinIO deployment consists of 4 or more drives/volumes managed by one or more minio server process, where the processes manage pooling the compute and storage resources into a single aggregated object storage resource. Each MinIO server has a complete picture of the distributed topology, such that an application can connect to any node in the deployment and perform S3 operations.

MinIO supports expanding an existing distributed deployment by adding a new Server Pool. Each Pool expands the total available storage capacity of the cluster while maintaining the overall availability of the cluster. Each Pool is its own failure domain, where the loss of one or more drives or nodes in that pool does not effect the availability of other pools in the deployment.

## Prerequisites

### Networking and Firewalls

Each node should have full bidirectional network access to every other node in the deployment. For containerized or orchestrated infrastructures, this may require specific configuration of networking and routing components such as ingress or load balancers. Certain operating systems may also require setting firewall rules. For example, the following command explicitly opens the default MinIO server API port 9000 on servers using firewalld:

firewall-cmd --permanent --zone=public --add-port=9000/tcp


All MinIO servers in the deployment must use the same listen port.

If you set a static MinIO Console port (e.g. :9001) you must also grant access to that port to ensure connectivity from external clients.

MinIO strongly recomends using a load balancer to manage connectivity to the cluster. The Load Balancer should use a “Least Connections” algorithm for routing requests to the MinIO deployment, since any MinIO node in the deployment can receive, route, or process client requests.

The following load balancers are known to work well with MinIO:

Configuring firewalls or load balancers to support MinIO is out of scope for this procedure. The Configure NGINX Proxy for MinIO Server reference provides a baseline configuration for using NGINX as a reverse proxy with basic load balancing configured.

### Sequential Hostnames

MinIO requires using expansion notation {x...y} to denote a sequential series of MinIO hosts when creating a server pool. MinIO therefore requires using sequentially-numbered hostnames to represent each minio server process in the pool.

Create the necessary DNS hostname mappings prior to starting this procedure. For example, the following hostnames would support a 4-node distributed server pool:

• minio5.example.com

• minio6.example.com

• minio7.example.com

• minio8.example.com

You can specify the entire range of hostnames using the expansion notation minio{5...8}.example.com.

Configuring DNS to support MinIO is out of scope for this procedure.

### Local JBOD Storage with Sequential Mounts

MinIO strongly recommends direct-attached JBOD arrays with XFS-formatted disks for best performance.

• Direct-Attached Storage (DAS) has significant performance and consistency advantages over networked storage (NAS, SAN, NFS).

• Deployments using non-XFS filesystems (ext4, btrfs, zfs) tend to have lower performance while exhibiting unexpected or undesired behavior.

• RAID or similar technologies do not provide additional resilience or availability benefits when used with distributed MinIO deployments, and typically reduce system performance.

Ensure all nodes in the server pool use the same type (NVMe, SSD, or HDD) of drive with identical capacity (e.g. N TB) . MinIO does not distinguish drive types and does not benefit from mixed storage types. Additionally. MinIO limits the size used per drive to the smallest drive in the deployment. For example, if the deployment has 15 10TB drives and 1 1TB drive, MinIO limits the per-drive capacity to 1TB.

MinIO requires using expansion notation {x...y} to denote a sequential series of drives when creating the new server pool, where all nodes in the server pool have an identical set of mounted drives. MinIO also requires that the ordering of physical drives remain constant across restarts, such that a given mount point always points to the same formatted drive. MinIO therefore strongly recommends using /etc/fstab or a similar file-based mount configuration to ensure that drive ordering cannot change after a reboot. For example:

$mkfs.xfs /dev/sdb -L DISK1$ mkfs.xfs /dev/sdc -L DISK2
$mkfs.xfs /dev/sdd -L DISK3$ mkfs.xfs /dev/sde -L DISK4

$nano /etc/fstab # <file system> <mount point> <type> <options> <dump> <pass> LABEL=DISK1 /mnt/disk1 xfs defaults,noatime 0 2 LABEL=DISK2 /mnt/disk2 xfs defaults,noatime 0 2 LABEL=DISK3 /mnt/disk3 xfs defaults,noatime 0 2 LABEL=DISK4 /mnt/disk4 xfs defaults,noatime 0 2  You can then specify the entire range of drives using the expansion notation /mnt/disk{1...4}. If you want to use a specific subfolder on each drive, specify it as /mnt/disk{1...4}/minio. MinIO does not support arbitrary migration of a drive with existing MinIO data to a new mount position, whether intentional or as the result of OS-level behavior. Network File System Volumes Break Consistency Guarantees MinIO’s strict read-after-write and list-after-write consistency model requires local drive filesystems (xfs, ext4, etc.). MinIO cannot provide consistency guarantees if the underlying storage volumes are NFS or a similar network-attached storage volume. For deployments that require using network-attached storage, use NFSv4 for best results. ### Minimum Drives for Erasure Code Parity MinIO requires each pool satisfy the deployment erasure code settings. Specifically the new pool topology must support a minimum of 2 x EC:N drives per erasure set, where EC:N is the Standard parity storage class of the deployment. This requirement ensures the new server pool can satisfy the expected SLA of the deployment. You can use the MinIO Erasure Code Calculator to check the Erasure Code Stripe Size (K+M) of your new pool. If the highest listed value is at least 2 x EC:N, the pool supports the deployment’s erasure parity settings. ## Considerations ### Writing Files MinIO does not automatically rebalance objects across the new server pools. Instead, MinIO performs new write operations to the pool with the most free storage weighted by the amount of free space on the pool divided by the free space across all available pools. The formula to determine the probability of a write operation on a particular pool is $$FreeSpaceOnPoolA / FreeSpaceOnAllPools$$ Consider a situation where a group of two pools has a total of 10 TiB of free space distributed as: • Pool A has 3 TiB of free space • Pool B has 2 TiB of free space • Pool C has 5 TiB of free space MinIO calculates the probability of a write operation to each of the pools as: • Pool A: 30% chance ($$3TiB / 10TiB$$) • Pool B: 20% chance ($$2TiB / 10TiB$$) • Pool C: 50% chance ($$5TiB / 10TiB$$) In addition to the free space calculation, if a write option (with parity) would bring a drive usage above 99% or a known free inode count below 1000, MinIO does not write to the pool. If desired, you can manually initiate a rebalance procedure with mc admin rebalance. For more about how rebalancing works, see managing objects across a deployment. Likewise, MinIO does not write to pools in a decommissioning process. ### Homogeneous Node Configurations MinIO strongly recommends selecting substantially similar hardware configurations for all nodes in the new server pool. Ensure the hardware (CPU, memory, motherboard, storage adapters) and software (operating system, kernel settings, system services) is consistent across all nodes in the pool. The new pool may exhibit unpredictable performance if nodes have heterogeneous hardware or software configurations. Workloads that benefit from storing aged data on lower-cost hardware should instead deploy a dedicated “warm” or “cold” MinIO deployment and transition data to that tier. The new server pool does not need to be substantially similar in hardware and software configuration to any existing server pool, though this may allow for simplified cluster management and more predictable performance across pools. See Production Hardware Requirements for more guidance on selecting hardware for MinIO deployments. ### Expansion is Non-Disruptive Adding a new server pool requires restarting all MinIO nodes in the deployment at around same time. MinIO strongly recommends restarting all nodes simultaneously. MinIO operations are atomic and strictly consistent. As such the restart procedure is non-disruptive to applications and ongoing operations. Do not perform “rolling” (e.g. one node at a time) restarts. ### Capacity-Based Planning MinIO generally recommends planning capacity such that server pool expansion is only required after 2+ years of deployment uptime. For example, consider an application suite that is estimated to produce 10TB of data per year. The current deployment is running low on free storage and therefore requires expansion to meet the ongoing storage demands of the application. The new server pool should provide at minimum 10TB + 10TB + 10TB = 30TB MinIO recommends adding buffer storage to account for potential growth in stored data (e.g. 40TB of total usable storage). The total planned usable storage in the deployment would therefore be ~80TB. As a rule-of-thumb, more capacity initially is preferred over frequent just-in-time expansion to meet capacity requirements. Since MinIO erasure coding requires some storage for parity, the total raw storage must exceed the planned usable capacity. Consider using the MinIO Erasure Code Calculator for guidance in planning capacity around specific erasure code settings. ## Expand a Distributed MinIO Deployment The following procedure adds a Server Pool to an existing MinIO deployment. Each Pool expands the total available storage capacity of the cluster while maintaining the overall availability of the cluster. All commands provided below use example values. Replace these values with those appropriate for your deployment. Review the Prerequisites before starting this procedure. Complete any planned hardware expansion prior to decommissioning older hardware pools. ### 1) Install the MinIO Binary on Each Node in the New Server Pool ### 2) Add TLS/SSL Certificates MinIO enables Transport Layer Security (TLS) 1.2+ automatically upon detecting a valid x.509 certificate (.crt) and private key (.key) in the MinIO ${HOME}/.minio/certs directory.

For systemd-managed deployments, use the $HOME directory for the user which runs the MinIO server process. The provided minio.service file runs the process as minio-user. The previous step includes instructions for creating this user with a home directory /home/minio-user. • Place TLS certificates into /home/minio-user/.minio/certs. • If any MinIO server or client uses certificates signed by an unknown Certificate Authority (self-signed or internal CA), you must place the CA certs in the /home/minio-user/.minio/certs/CAs on all MinIO hosts in the deployment. MinIO rejects invalid certificates (untrusted, expired, or malformed). If the minio.service file specifies a different user account, use the $HOME directory for that account. Alternatively, specify a custom certificate directory using the minio server --certs-dir commandline argument. Modify the MINIO_OPTS variable in /etc/defaults/minio to set this option. The systemd user which runs the MinIO server process must have read and listing permissions for the specified directory.

For more specific guidance on configuring MinIO for TLS, including multi-domain support via Server Name Indication (SNI), see Network Encryption (TLS). You can optionally skip this step to deploy without TLS enabled. MinIO strongly recommends against non-TLS deployments outside of early development.

### 3) Create the systemd Service File

The .deb or .rpm packages install the following systemd service file to /etc/systemd/system/minio.service. For binary installations, create this file manually on all MinIO hosts:

[Unit]
Description=MinIO
Documentation=https://min.io/docs/minio/linux/index.html
Wants=network-online.target
After=network-online.target
AssertFileIsExecutable=/usr/local/bin/minio

[Service]
WorkingDirectory=/usr/local

User=minio-user
Group=minio-user
ProtectProc=invisible

EnvironmentFile=-/etc/default/minio
ExecStartPre=/bin/bash -c "if [ -z \"${MINIO_VOLUMES}\" ]; then echo \"Variable MINIO_VOLUMES not set in /etc/default/minio\"; exit 1; fi" ExecStart=/usr/local/bin/minio server$MINIO_OPTS $MINIO_VOLUMES # Let systemd restart this service always Restart=always # Specifies the maximum file descriptor number that can be opened by this process LimitNOFILE=65536 # Specifies the maximum number of threads this process can create TasksMax=infinity # Disable timeout logic and wait until process is stopped TimeoutStopSec=infinity SendSIGKILL=no [Install] WantedBy=multi-user.target # Built for${project.name}-${project.version} (${project.name})


The minio.service file runs as the minio-user User and Group by default. You can create the user and group using the groupadd and useradd commands. The following example creates the user, group, and sets permissions to access the folder paths intended for use by MinIO. These commands typically require root (sudo) permissions.

groupadd -r minio-user
useradd -M -r -g minio-user minio-user
chown minio-user:minio-user /mnt/disk1 /mnt/disk2 /mnt/disk3 /mnt/disk4


The specified drive paths are provided as an example. Change them to match the path to those drives intended for use by MinIO.

Alternatively, change the User and Group values to another user and group on the system host with the necessary access and permissions.

MinIO publishes additional startup script examples on github.com/minio/minio-service.

### 4) Create the Service Environment File

Create an environment file at /etc/default/minio. The MinIO service uses this file as the source of all environment variables used by MinIO and the minio.service file.

The following examples assumes that:

• The deployment has a single server pool consisting of four MinIO server hosts with sequential hostnames.

minio1.example.com   minio3.example.com
minio2.example.com   minio4.example.com


Each host has 4 locally attached drives with sequential mount points:

/mnt/disk1/minio   /mnt/disk3/minio
/mnt/disk2/minio   /mnt/disk4/minio

• The new server pool consists of eight new MinIO hosts with sequential hostnames:

minio5.example.com   minio9.example.com
minio6.example.com   minio10.example.com
minio7.example.com   minio11.example.com
minio8.example.com   minio12.example.com

• All hosts have eight locally-attached drives with sequential mount-points:

/mnt/disk1/minio  /mnt/disk5/minio
/mnt/disk2/minio  /mnt/disk6/minio
/mnt/disk3/minio  /mnt/disk7/minio
/mnt/disk4/minio  /mnt/disk8/minio

• The deployment has a load balancer running at https://minio.example.net that manages connections across all MinIO hosts. The load balancer should not be routing requests to the new hosts at this step, but should have the necessary configuration updates planned.

Modify the example to reflect your deployment topology:

# Set the hosts and volumes MinIO uses at startup
# The command uses MinIO expansion notation {x...y} to denote a
# sequential series.
#
# The following example starts the MinIO server with two server pools.
#
# The space delimiter indicates a seperate server pool
#
# The second set of hostnames and volumes is the newly added pool.
# The pool has sufficient stripe size to meet the existing erasure code
# parity of the deployment (2 x EC:4)
#
# The command includes the port on which the MinIO servers listen for each
# server pool.

MINIO_VOLUMES="https://minio{1...4}.example.net:9000/mnt/disk{1...4}/minio https://minio{5...12}.example.net:9000/mnt/disk{1...8}/minio"

# Set all MinIO server options
#
# The following explicitly sets the MinIO Console listen address to
# port 9001 on all network interfaces. The default behavior is dynamic
# port selection.

# Set the root username. This user has unrestricted permissions to
# perform S3 and administrative API operations on any resource in the
# deployment.
#

#
# Use a long, random, unique string that meets your organizations

# Set to the URL of the load balancer for the MinIO deployment
# This value *must* match across all MinIO servers. If you do
# not have a load balancer, set this value to to any *one* of the
# MinIO hosts in the deployment as a temporary measure.
MINIO_SERVER_URL="https://minio.example.net:9000"


You may specify other environment variables or server commandline options as required by your deployment. All MinIO nodes in the deployment should include the same environment variables with the matching values.

### 5) Restart the MinIO Deployment with Expanded Configuration

Issue the following commands on each node simultaneously in the deployment to restart the MinIO service:

sudo systemctl restart minio.service


Use the following commands to confirm the service is online and functional:

sudo systemctl status minio.service
journalctl -f -u minio.service


MinIO may log an increased number of non-critical warnings while the server processes connect and synchronize. These warnings are typically transient and should resolve as the deployment comes online.

MinIO strongly recommends restarting all nodes simultaneously. MinIO operations are atomic and strictly consistent. As such the restart procedure is non-disruptive to applications and ongoing operations.

Do not perform “rolling” (e.g. one node at a time) restarts.

### 6) Next Steps

• Update any load balancers, reverse proxies, or other network control planes to route client requests to the new hosts in the MinIO distributed deployment. While MinIO automatically manages routing internally, having the control planes handle initial connection management may reduce network hops and improve efficiency.

• Review the MinIO Console to confirm the updated cluster topology and monitor performance.