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Pre-deployment Checklist

This section covers the preliminary setup required on the compute and storage nodes before deploying DAOS.

Enable IOMMU

In order to run the DAOS server as a non-root user with NVMe devices, the hardware must support virtualized device access, and it must be enabled in the system BIOS. On IntelĀ® systems, this capability is named IntelĀ® Virtualization Technology for Directed I/O (VT-d). Once enabled in BIOS, IOMMU support must also be enabled in the Linux kernel. Exact details depend on the distribution, but the following example should be illustrative:

# Enable IOMMU on CentOS 7 and EL 8
# All commands must be run as root/sudo!

$ sudo vi /etc/default/grub # add the following line:
GRUB_CMDLINE_LINUX_DEFAULT="intel_iommu=on"

# after saving the file, run the following to reconfigure
# the bootloader:
$ sudo grub2-mkconfig --output=/boot/grub2/grub.cfg

# if the command completed with no errors, reboot the system
# in order to make the changes take effect
$ sudo reboot

Note

To force SPDK to use UIO rather than VFIO at daos_server runtime, set 'disable_vfio' in the server config file, but note that this will require running daos_server as root.

Warning

If VFIO is not enabled on RHEL 8.x and derivatives, you will run into the issue described in: https://github.com/spdk/spdk/issues/1153

The problem manifests with the following signature in the kernel logs:

[82734.333834] genirq: Threaded irq requested with handler=NULL and !ONESHOT for irq 113 [82734.341761] uio_pci_generic: probe of 0000:18:00.0 failed with error -22

As a consequence, the use of VFIO on these distributions is a requirement since UIO is not supported.

Time Synchronization

The DAOS transaction model relies on timestamps and requires time to be synchronized across all the storage nodes. This can be done using NTP or any other equivalent protocol.

User and Group Management

DAOS User/Groups on the Servers

The daos_server and daos_engine processes run under a non-privileged userid daos_server. If that user does not exist at the time the daos-server RPM is installed, the user will be created as part of the RPM installation. A group daos-server will also be created as its primary group, as well as two additional groups daos_metrics and daos_daemons to which the daos_server user will be added.

If there are site-specific rules for the creation of users and groups, it is advisable to create these users and groups following the site-specific conventions before installing the daos-server RPM.

DAOS User/Groups on the Clients

The daos_agent process runs under a non-privileged userid daos_agent. If that user does not exist at the time the daos-client RPM is installed, the user will be created as part of the RPM installation. A group daos-agent will also be created as its primary group, as well as an additional group daos_daemons to which the daos_agent user will be added.

If there are site-specific rules for the creation of users and groups, it is advisable to create these users and groups following the site-specific conventions before installing the daos-client RPM.

User/Group Synchronization for End Users

DAOS ACLs for pools and containers store the actual user and group names (instead of numeric IDs). Therefore the servers do not need access to a synchronized user/group database. The DAOS Agent (running on the client nodes) is responsible for resolving a user's UID/GID to user/group names, which are then added to a signed credential and sent to the DAOS storage nodes.

With libfabric, it is not supported to aggregate (or stripe over) multiple network links as a single endpoint. So a single DAOS engine can only use a single network link. But when a storage node runs multiple engine instances, each engine instance can and should manage its own network link to achieve optimum performance.

Subnet

Since all engines need to be able to communicate, the different network interfaces must be on the same subnet or you must configuring routing across the different subnets.

Infiniband Settings

Some special configuration is required to configure the IP layer and to use librdmacm with multiple interfaces in the same IP network.

First, the accept_local feature must be enabled on the network interfaces to be used by DAOS. This can be done using the following command ( must be replaced with the interface names):

$ sudo sysctl -w net.ipv4.conf.all.accept_local=1

Second, Linux must be configured to only send ARP replies on the interface targeted in the ARP request. This is configured via the arp_ignore parameter. This should be set to 2 if all the IPoIB interfaces on the client and storage nodes are in the same logical subnet (e.g. ib0 == 10.0.0.27, ib1 == 10.0.1.27, prefix=16).

$ sysctl -w net.ipv4.conf.all.arp_ignore=2

If separate logical subnets are used (e.g. prefix = 24), then the value must be set to 1.

$ sysctl -w net.ipv4.conf.all.arp_ignore=1

Finally, the rp_filter is set to 1 by default on several distributions (e.g. on CentOS 7 and EL 8) and should be set to either 0 or 2, with 2 being more secure. This is true even if the configuration uses a single logical subnet.

$ sysctl -w net.ipv4.conf.<ifaces>.rp_filter=2

All those parameters can be made persistent in /etc/sysctl.conf by adding a new sysctl file under /etc/sysctl.d (e.g. /etc/sysctl.d/95-daos-net.conf) with all the relevant settings.

For more information, please refer to the librdmacm documentation

Install from Source

When DAOS is installed from source (and not from pre-built packages), extra manual settings detailed in this section are required.

Runtime Directory Setup

DAOS uses a series of Unix Domain Sockets to communicate between its various components. On modern Linux systems, Unix Domain Sockets are typically stored under /run or /var/run (usually a symlink to /run) and are a mounted tmpfs file system. There are several methods for ensuring the necessary directories are setup.

A sign that this step may have been missed is when starting daos_server or daos_agent, you may see the message:

$ mkdir /var/run/daos_server: permission denied
Unable to create socket directory: /var/run/daos_server

Non-default Directory

By default, daos_server and daos_agent will use the directories /var/run/daos_server and /var/run/daos_agent respectively. To change the default location that daos_server uses for its runtime directory, uncomment and set the socket_dir configuration value in /etc/daos/daos_server.yml. For the daos_agent, either uncomment and set the runtime_dir configuration value in /etc/daos/daos_agent.yml or a location can be passed on the command line using the --runtime_dir flag (daos_agent -d /tmp/daos_agent).

Warning

Do not change these when running under systemd control. If these directories need to be changed, insure they match the RuntimeDirectory setting in the /usr/lib/systemd/system/daos_agent.service and /usr/lib/systemd/system/daos_server.service configuration files. The socket directories will be created and removed by systemd when the services are started and stopped.

Default Directory (non-persistent)

Files and directories created in /run and /var/run only survive until the next reboot. These directories are required for subsequent runs; therefore, if reboots are infrequent, an easy solution while still utilizing the default locations is to create the required directories manually. To do this execute the following commands.

daos_server:

$ mkdir /var/run/daos_server
$ chmod 0755 /var/run/daos_server
$ chown user:user /var/run/daos_server (where user is the user you
    will run daos_server as)

daos_agent:

$ mkdir /var/run/daos_agent
$ chmod 0755 /var/run/daos_agent
$ chown user:user /var/run/daos_agent (where user is the user you
    will run daos_agent as)

Default Directory (persistent)

The following steps are not necessary if DAOS is installed from rpms.

If the server hosting daos_server or daos_agent will be rebooted often, systemd provides a persistent mechanism for creating the required directories called tmpfiles.d. This mechanism will be required every time the system is provisioned and requires a reboot to take effect.

To tell systemd to create the necessary directories for DAOS:

  • Copy the config file: cp utils/systemd/daosfiles.conf /etc/tmpfiles.d

  • Modify the copied file to change the user and group fields (currently daos) to the user daos will be run as

  • Reboot the system, and the directories will be created automatically on all subsequent reboots.

Privileged Helper

DAOS employs a privileged helper binary (daos_admin) to perform tasks that require elevated privileges on behalf of daos_server.

When DAOS is installed from RPM, the daos_admin helper is automatically installed to the correct location with the correct permissions. The RPM creates a daos_server system group and configures permissions such that daos_admin may only be invoked from daos_server.

For non-RPM installations, there are two supported scenarios:

  1. daos_server is run as root, which means that daos_admin is also invoked as root, and therefore no additional setup is necessary.
  2. daos_server is run as a non-root user, which means that daos_admin must be manually installed and configured.

The steps to enable the second scenario are as follows (steps are assumed to be running out of a DAOS source tree which may be on a NFS share):

$ chmod -x $daospath/bin/daos_admin # prevent this copy from being executed
$ sudo cp $daospath/bin/daos_admin /usr/bin/daos_admin
$ sudo chmod 4755 /usr/bin/daos_admin # make this copy setuid root
$ sudo mkdir -p /usr/share/daos/control # create symlinks to SPDK scripts
$ sudo ln -sf $daospath/share/daos/control/setup_spdk.sh \
           /usr/share/daos/control
$ sudo mkdir -p /usr/share/spdk/scripts
$ sudo ln -sf $daospath/share/spdk/scripts/setup.sh \
           /usr/share/spdk/scripts
$ sudo ln -sf $daospath/share/spdk/scripts/common.sh \
           /usr/share/spdk/scripts
$ sudo ln -s $daospath/include \
           /usr/share/spdk/include

Note

The RPM installation is preferred for production scenarios. Manual installation is most appropriate for development and predeployment proof-of-concept scenarios.

Memory Lock Limits

Low ulimit for memlock can cause SPDK to fail and emit the following error:

daos_engine:1 EAL: cannot set up DMA remapping, error 12 (Cannot allocate
    memory)

The memlock limit only needs to be manually adjusted when daos_server is not running as a systemd service. Default ulimit settings vary between OSes.

For RPM installations, the service will typically be launched by systemd and the limit is pre-set to unlimited in the daos_server.service unit file

Note that values set in /etc/security/limits.conf are ignored by services launched by systemd.

For non-RPM installations where daos_server is launched directly from the commandline (including source builds), limits should be adjusted in /etc/security/limits.conf as per this article (which is a RHEL specific document but the instructions apply to most Linux distributions).

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