Memory and Disk Space
Minimum Memory
A minimum of 8 GB total memory is required on a node. MapR recommends at least 16 GB for a production environment, and typical MapR production nodes have 32 GB or more.
Run free -g
to display total and available memory in gigabytes.
$ free -g
total used free shared buffers cached
Mem: 3 2 1 0 0 1
-/+ buffers/cache: 0 2
Swap: 2 0 2
If the free
command is not found, there are many alternatives: grep
MemTotal: /proc/meminfo
, vmstat -s -SM
, top
, or
various GUI system information tools.
MapR does not recommend using the numad service, since it has not been tested and validated with MapR. Using numad can cause artificial memory constraints to be set which can lead to performance degradation under load. To disable numad:
- Stop the service by issuing the command
service numad stop
. - Set the numad service not to start on reboot:
chkconfig numad off
MapR does not recommend using overcommit because it may lead to the kernel memory
manager killing processes to free memory, resulting in killed MapR processes and system
instability. Set vm.overcommit_memory
to 0:
- Edit the file
/etc/sysctl.conf
and add the following line: vm.overcommit_memory=0 - Save the file and run: sysctl -p
Storage
MapR manages raw, unformatted devices directly to optimize performance and offer high availability. For data nodes, allocate at least 3 unmounted physical drives or partitions for MapR storage. MapR uses disk spindles in parallel for faster read/write bandwidth and therefore groups disks into sets of three.
Drive Configuration
Do not use RAID or Logical Volume Management with disks that will be added to MapR. While MapR supports these technologies, using them incurs additional setup overhead and can affect your cluster's performance. Due to the possible formatting requirements that are associated with changes to the drive settings, configure the drive settings prior to installing MapR.
If you have a RAID controller, configure it to run in HBA mode. For LSI MegaRAID controllers that do not support HBA, configure the following drive group settings for optimal performance:
Property (The actual name depends on the version) | Recommended Setting |
---|---|
RAID Level | RAID0 |
Stripe Size | >=256K |
Cache Policy or I/O Policy | Cached IO or Cached |
Read Policy | Always Read Ahead or Read Ahead |
Write Policy | Write-Through |
Disk Cache Policy or Drive Cache | Disabled |
Minimum Disk Space
OS Partition. Provide at least 10 GB of free disk space on the operating system partition.
MapR-FS. Provide at least 8 GB of free disk space for MapR-FS.
Disk. Provide 10 GB of free disk space in the /tmp
directory and 128
GB of free disk space in the /opt
directory. Services, such as JobTracker and
TaskTracker, use the /tmp
directory. Files, such as logs and cores, use the
/opt
directory.
Swap space. Provide sufficient swap space for stability, 10% more than the node's physical memory, but not less than 24 GB and not more than 128 GB.
ZooKeeper. On ZooKeeper nodes, dedicate a partition, if practicable, for the
/opt/mapr/zkdata
directory to avoid other processes filling that partition
with writes and to reduce the possibility of errors due to a full
/opt/mapr/zkdata
directory. This directory is used to store snapshots that
are up to 64 MB. Since the four most recent snapshots are retained, reserve at least 500 MB
for this partition. Do not share the physical disk where /opt/mapr/zkdata
resides with any MapR File System data partitions to avoid I/O conflicts that might lead to
ZooKeeper service failures.