Operating System Requirements

MongoDB can be deployed on a number of platforms. A platform consists of a CPU architecture and operating system. The current supported platforms can be found in the MongoDB documentation.

The relevant operating system and associated recommendations can be found below :

Operating System	Recommendations
Red Hat Enterprise Linux/ CentOS / Oracle Linux/Ubuntu/SUSE/Debian	The recommended settings for Linux operating systems can be found in theLinux Recommended Settings. In addition to the existing best practices ensure that the number of requests per volume is set to a higher value. Increasing this value allows individual volumes to service more storage requests at any single time. Add the following to the udev rules file for FlashArray to increase the maximum number of requests for a single volume: `Set DM devices number of requests to 1024 or higher. This uses 1MB of memory per request ACTION=="add\|change", KERNEL=="dm-[0-9]", SUBSYSTEM=="block", ENV{DM_NAME}=="3624a937", ATTR{queue/nr_requests}="1024"`
Microsoft Windows Server	The best practices for Microsoft Windows can be set using the Validate Windows Server with Test-Pfa2WindowsBestPractices Cmdlet.

Operating System

Recommendations

Red Hat Enterprise Linux/ CentOS / Oracle Linux/Ubuntu/SUSE/Debian

The recommended settings for Linux operating systems can be found in theLinux Recommended Settings.

In addition to the existing best practices ensure that the number of requests per volume is set to a higher value. Increasing this value allows individual volumes to service more storage requests at any single time.

Add the following to the udev rules file for FlashArray to increase the maximum number of requests for a single volume:


Set DM devices number of requests to 1024 or higher. This uses 1MB of memory per request
ACTION=="add|change", KERNEL=="dm-[0-9]*", SUBSYSTEM=="block", ENV{DM_NAME}=="3624a937*", ATTR{queue/nr_requests}="1024"

Microsoft Windows Server

The best practices for Microsoft Windows can be set using the Validate Windows Server with Test-Pfa2WindowsBestPractices Cmdlet.

File System Configuration

The recommended file systems for MongoDB with FlashArray are NTFS (Microsoft Windows) , and XFS (Linux).

Microsoft Windows

The default allocation unit size (4K) for NTFS filesystems works well with MongoDB.

Linux

XFS

When using the XFS file system for any MongoDB database files the default options are typically all that is required.

XFS file systems can be created on a FlashArray volume using the command:


mkfs.xfs /dev/mapper/<device>

The discard and noatime options in /etc/fstab should be used with XFS in the majority of cases.


/dev/mapper/<device> /mountpoint xfs discard,noatime 0 0

If using iSCSI connectivity to FlashArray ensure the _netdev,nofail options are present:


/dev/mapper/<device> /mountpoint xfs _netdev,nofail,discard,noatime 0 0

For systems using the Linux Kernel 4.13 or later the "nobarrier" option is deprecated for XFS. To increase the possible performance of the volume add the following udev rule to the existing rules file:

FCP and iSCSI


ACTION=="add|change", KERNEL=="sd*[!0-9]", SUBSYSTEM=="block", ENV{ID_VENDOR}=="PURE", ATTR{queue/write_cache}="write through"
ACTION=="add|change", KERNEL=="dm-[0-9]*", SUBSYSTEM=="block", ENV{DM_NAME}=="3624a937*", ATTR{queue/write_cache}="write through"

NVMe-oF connectivity


ACTION=="add|change", KERNEL=="nvme*[!0-9]", SUBSYSTEM=="block", ATTR{queue/write_cache}="write through"
ACTION=="add|change", KERNEL=="dm-[0-9]*", SUBSYSTEM=="block", ENV{DM_NAME}=="eui.00723ec7b5b427*", ATTR{queue/write_cache}= "write through"

Once the rules have been added reload and apply them using the udevadm utility:


 udevadm control --reload-rules && udevadm trigger

Adding an entry to /etc/fstab

Entries in /etc/fstab can be done using the device path or the UUID of the filesystem.

To get the UUID of a file system use the blkid command and match the device to the respective UUID.


[root@DB-01 ~]# blkid
/dev/sdb: PTUUID="91360acd-7332-47d9-9027-0300c7e3a081" PTTYPE="gpt"
/dev/sda: PTUUID="91360acd-7332-47d9-9027-0300c7e3a081" PTTYPE="gpt"
/dev/sdc: PTUUID="91360acd-7332-47d9-9027-0300c7e3a081" PTTYPE="gpt"
/dev/mapper/3624a93708488b6dac70f42a20001ec55: PTUUID="91360acd-7332-47d9-9027-0300c7e3a081" PTTYPE="gpt"
/dev/sdd: PTUUID="91360acd-7332-47d9-9027-0300c7e3a081" PTTYPE="gpt"
/dev/mapper/3624a93708488b6dac70f42a20001ec55p1: UUID="D759-B5A6" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="EFI System Partition" PARTUUID="8f317ff7-97f5-48ab-83d8-f54d647fb390"
/dev/mapper/3624a93708488b6dac70f42a20001ec55p2: UUID="97d13054-20c7-436e-b6ab-ef8b8f3ce46b" BLOCK_SIZE="512" TYPE="xfs" PARTUUID="2644a548-dde5-4ac8-8679-c100011a0d78"
/dev/mapper/3624a93708488b6dac70f42a20001ec55p3: UUID="GXujto-h3yl-V3hq-jFZs-3xd6-RhLB-0vFf8l" TYPE="LVM2_member" PARTUUID="380fbf39-eb6e-4bf0-ae25-f4abd6f02803"
/dev/mapper/rhel-root: UUID="5547b1a3-590a-4d54-9d0b-710714ca7e52" BLOCK_SIZE="512" TYPE="xfs"
/dev/mapper/rhel-swap: UUID="70470107-9368-4d32-82d8-7620f1cdc665" TYPE="swap"
/dev/mapper/rhel-home: UUID="0e08dae8-3d93-451c-a021-b3fe58f9b464" BLOCK_SIZE="512" TYPE="xfs"
/dev/nvme0n1: UUID="36202f29-95e8-49d2-a200-4057712b9236" BLOCK_SIZE="512" TYPE="xfs"
/dev/nvme0n2: UUID="489e7195-46b5-466a-8770-9aa7938c8afb" BLOCK_SIZE="512" TYPE="xfs"
/dev/mapper/eui.00668f1ab9b15f4b24a937c400011884: UUID="36202f29-95e8-49d2-a200-4057712b9236" BLOCK_SIZE="512" TYPE="xfs"
/dev/nvme1n1: UUID="36202f29-95e8-49d2-a200-4057712b9236" BLOCK_SIZE="512" TYPE="xfs"
/dev/nvme3n5: UUID="41e4a009-b98a-4d48-9d69-f45e717485e2" BLOCK_SIZE="512" TYPE="xfs"
/dev/mapper/eui.00668f1ab9b15f4b24a937c400011890: UUID="489e7195-46b5-466a-8770-9aa7938c8afb" BLOCK_SIZE="512" TYPE="xfs"
/dev/mapper/eui.00668f1ab9b15f4b24a937c400011898: UUID="0f4da946-a86e-4fd3-bcd3-0d74d88ef83b" BLOCK_SIZE="512" TYPE="xfs"
/dev/mapper/eui.00668f1ab9b15f4b24a937c4000118a0: UUID="9a5e14cc-b226-4f7c-91a5-f8397a73b5bd" BLOCK_SIZE="512" TYPE="xfs"
/dev/mapper/eui.00668f1ab9b15f4b24a937c4000118a1: UUID="41e4a009-b98a-4d48-9d69-f45e717485e2" BLOCK_SIZE="512" TYPE="xfs"

Then use the UUID in place of the device path:


UUID=489e7195-46b5-466a-8770-9aa7938c8afb /mountpoint xfs _netdev,nofail,noatime,discard 0 0

Increase file limits

The file limits (ulimit) settings for UNIX platforms may need to be adjusted based on the workload requirements. To do this edit /etc/security/limits.conf and add the following before the end of the file :


mongod           soft    nproc           64000
mongod           hard    nproc           64000
mongod           soft    nofile          64000
mongod           hard    nofile          64000

Once edited , save the file and reboot the system.

Lower readahead values

MongoDB disk access patterns are generally random and thus does not require filesystem data to be cached for sequental read operations.

Using the blockdev --report command the readahead setting can be found on a per block device basis :


blockdev --report
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw  8192   512  4096          0   4398046511104   /dev/sdn
rw  8192   512  4096          0    824633720832   /dev/sdp
rw  8192   512  4096          0   4398046511104   /dev/sdt
rw  8192   512  4096          0    824633720832   /dev/sds
rw  8192   512  4096          0   4398046511104   /dev/sdq
rw  8192   512  4096          0    824633720832   /dev/sdv
rw  8192   512  4096          0     53687091200   /dev/sdu
rw  8192   512  4096          0   4398046511104   /dev/sdw
rw  8192   512  4096          0     53687091200   /dev/sdx
rw  8192   512  4096          0    824633720832   /dev/dm-0
rw  8192   512  4096          0   4398046511104   /dev/dm-1

In this example /dev/dm-1 is the multipath device on which the MongoDB data files will reside.

To ensure the readahead values are persistently set for this device a udev rule will be created for it. To find the device name for the udev rule we need to query it using udeadm. Using the command udevadm info <device> the DM_NAME value can be found :


udevadm info /dev/dm-1
P: /devices/virtual/block/dm-1
N: dm-1
L: 50
S: disk/by-id/dm-name-3624a9370f2abf1c1b1c049fd000153b8
S: disk/by-id/dm-uuid-mpath-3624a9370f2abf1c1b1c049fd000153b8
S: disk/by-id/scsi-3624a9370f2abf1c1b1c049fd000153b8
S: disk/by-id/wwn-0x624a9370f2abf1c1b1c049fd000153b8
S: disk/by-uuid/45cdb491-820c-44c6-89f2-2a75ffca0a48
S: mapper/3624a9370f2abf1c1b1c049fd000153b8
E: DEVLINKS=/dev/disk/by-id/wwn-0x624a9370f2abf1c1b1c049fd000153b8 /dev/disk/by-id/dm-uuid-mpath-3624a9370f2abf1c1b1c049fd000153b8 /dev/mapper/3624a9370f2abf1c1b1c049fd000153b8 /dev/disk/by-uuid/45cdb491-820c-44c6-89f2-2a75ffca0a48 /dev/disk/by-id/scsi-3624a9370f2abf1c1b1c049fd000153b8 /dev/disk/by-id/dm-name-3624a9370f2abf1c1b1c049fd000153b8
E: DEVNAME=/dev/dm-1
E: DEVPATH=/devices/virtual/block/dm-1
E: DEVTYPE=disk
E: DM_ACTIVATION=0
E: DM_NAME=3624a9370f2abf1c1b1c049fd000153b8
E: DM_SERIAL=3624a9370f2abf1c1b1c049fd000153b8
E: DM_SUBSYSTEM_UDEV_FLAG0=1
E: DM_SUSPENDED=0
E: DM_TYPE=scsi
E: DM_UDEV_DISABLE_LIBRARY_FALLBACK_FLAG=1
E: DM_UDEV_PRIMARY_SOURCE_FLAG=1
E: DM_UDEV_RULES_VSN=2
E: DM_UUID=mpath-3624a9370f2abf1c1b1c049fd000153b8
E: DM_WWN=0x624a9370f2abf1c1b1c049fd000153b8
E: ID_FS_TYPE=xfs
E: ID_FS_USAGE=filesystem
E: ID_FS_UUID=45cdb491-820c-44c6-89f2-2a75ffca0a48
E: ID_FS_UUID_ENC=45cdb491-820c-44c6-89f2-2a75ffca0a48
E: MAJOR=253
E: MINOR=1
E: MPATH_DEVICE_READY=1
E: MPATH_SBIN_PATH=/sbin
E: MPATH_UNCHANGED=1
E: SUBSYSTEM=block
E: TAGS=:systemd:
E: USEC_INITIALIZED=5992667

Once the DM_NAME has been obtained update an existing rules file in /etc/udev/rules.d/ or create a new one with the below entry :


ACTION=="add|change", KERNEL=="dm-[0-9]*", SUBSYSTEM=="block", ENV{DM_NAME}=="3624a9370f2abf1c1b1c049fd000153b8", ATTR{bdi/read_ahead_kb}="32"

To apply the changes execute the following :


udevadm control --reload-rules && udevadm trigger

Once the changes have been aplied to the relevant volumes then blockdev --report should show the RA (Read Ahead) value to be the same as that set in the udev rules.


blockdev --report
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw  8192   512  4096          0   4398046511104   /dev/sdn
rw  8192   512  4096          0    824633720832   /dev/sdp
rw  8192   512  4096          0   4398046511104   /dev/sdt
rw  8192   512  4096          0    824633720832   /dev/sds
rw  8192   512  4096          0   4398046511104   /dev/sdq
rw  8192   512  4096          0    824633720832   /dev/sdv
rw  8192   512  4096          0     53687091200   /dev/sdu
rw  8192   512  4096          0   4398046511104   /dev/sdw
rw  8192   512  4096          0     53687091200   /dev/sdx
rw    32   512  4096          0    824633720832   /dev/dm-0
rw    32   512   512          0     53687091200   /dev/dm-1