Set your configuration options to maximize the performance of a target host in a Delphix engine deployment. These network-tuning changes should improve performance for any data source

Linux/Redhat/CentOs

Tune the Kernel NFS client

In Linux, the number of simultaneous NFS requests is limited by the Remote Procedure Call (RPC) subsystem. The maximum number of simultaneous requests defaults to 16. Maximize the number of simultaneous requests by changing the kernel tunable sunrpc.tcp_slot_table_entries value to 128.

To ensure that the interface does not drop packets because the driver is configured with one receive queue, use the following commands to view the adaptor policy/increase Rx queue length:

<LinuxHost> $ ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:22:BB:CC:DD:22
          inet addr:www.xxx.yyy.zzz  Bcast:www.xxx.yyy.zzz  Mask:255.255.255.0
          inet6 addr: feee::222:bbff:fffc:ddd/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
          RX packets:760729910 errors:0 dropped:700 overruns:0 frame:0
          TX packets:309094054 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1023150307866 (952.8 GiB)  TX bytes:190673864056 (177.5 GiB)
RHEL4 through RHEL5.6

  1. As a superuser, run the following command to change the instantaneous value of simultaneous RPC commands:

    # sysctl -w sunrpc.tcp_slot_table_entries=128

  2. Edit the file /etc/modprobe.d/modprobe.conf.dist and change the line:

    install sunrpc /sbin/modprobe --first-time --ignore-install sunrpc && { /bin/mount -t rpc_pipefs sunrpc /var/lib/nfs/rpc_pipefs > /dev/null2>&1 || :;

    to

    install sunrpc /sbin/modprobe --first-time --ignore-install sunrpc && { /bin/mount -t rpc_pipefs sunrpc /var/lib/nfs/rpc_pipefs > /dev/null2>&1 ; /sbin/sysctl -w sunrpc.tcp_slot_table_entries=128; }

    Improper changes to the modprobe.conf.dist file may disrupt the use of NFS on the system. Check with your system administrator or operating system vendor for assistance. Save a copy of the modprobe.conf.dist in a directory other than /etc/modprobe.d before starting.

RHEL 5.7 through RHEL 6.2

  1. As a superuser, run the following command to change the instantaneous value of simultaneous RPC commands:

    # sysctl -w sunrpc.tcp_slot_table_entries=128

  2. If it doesn't already exist, create the file /etc/modprobe.d/rpcinfowith the following contents:

    options sunrpc tcp_slot_table_entries=128
RHEL 6.3 onwards

Beginning with RHEL 6.3, the number of RPC slots is dynamically managed by the system and does not need to be tuned. Although the sunrpc.tcp_slot_table_entries tuneable still exists, it has a default value of 2, instead of 16 as in prior releases. The maximum number of simultaneous requests is determined by the new tuneable, sunrpc.tcp_max_slot_table_entries which has a default value of 65535.

Tune TCP optimizations for high throughput

For high-throughput, high-latency operations such as NFS, the Linux TCP stack may require additional tuning to ensure optimal performance. The following kernel parameters improve socket buffer usage, reduce retransmission overhead, and allow the TCP window to scale effectively. These recommendations apply across major Linux distributions.

System administrators may apply these settings using either /etc/sysctl.conf or a distribution-specific fileunder /etc/sysctl.d/. Delphix does not require a specific implementation method.

TCP Buffers

Increase the read/write buffer sizes to support high-throughput IO operations.

net.ipv4.tcp_rmem = 4096 16777216 16777216
net.ipv4.tcp_wmem = 4096 4194304 16777216

TCP Selective Acknowledgments (SACK)

Enable selective acknowledgment to reduce retransmission overhead and improve efficiency.

net.ipv4.tcp_sack = 1

Automatic TCP Window Scaling

Allow dynamic window scaling to adapt to variable network performance conditions.

net.ipv4.tcp_window_scaling = 1

TCP Timestamps

Enable timestamps to aid round-trip time measurement and retransmission control.

net.ipv4.tcp_timestamps = 1

Applying the Settings

After updating your sysctl configuration file, apply the new values:

sysctl -p

NFSv4 only - enable recover lost locks  

RHEL 6.6 onwards

By default, the Redhat NFSv4 client does not attempt to reclaim locks that were lost due to a lease expiration event. This can cause an application to encounter unexpected EIO errors on system calls such as write. The Delphix use case requires the NFSv4 client to attempt to reclaim lost locks that were due to lease expiration. An NFS client module parameter, 'recover_lost_locks', is used to change the default behavior. Use the following command to check if the "recover_lost_locks" option is set to 1:

grep recover_lost_locks /etc/modprobe.d/*.conf

If the option is currently set to 0, change it to 1. If it is missing, as a superuser, run the following two commands to enable the NFS client to recover the lost locks feature:

# cat > /etc/modprobe.d/nfs4-locks.conf <<EOF
options nfs recover_lost_locks=1
EOF
 
# [ -d "/sys/module/nfs" ] && echo Y > /sys/module/nfs/parameters/recover_lost_locks

IBM AIX® 

AIX systems

While NFSv4 no longer uses the portmap (or rpcbind) service for network communication, and firewalls do not need to allow traffic on port 111, the portmap service must still be running locally on both the AIX client and the Delphix engine.

Disabling the portmap daemon can prevent NFSv4 mounts from working correctly on AIX, even if everything else is configured properly.

AIX NFSv4 configuration requirements (7.2 and 7.3)

  1. An NFS Domain must be configured.

  2. The nfsrgyd service must be running.

  3. The NFS server IP address from the Delphix Engine must be mappable to an FQDN.

  4. Configure the nfsv4 domain on the AIX target host bash-3.2# chnfsdom test.com.

  5. Start the nfsrgyd service and confirm it is active:

    bash-3.2# startsrc -s nfsrgyd

bash-3.2# lssrc -s nfsrgyd
Subsystem         Group            PID          Status
 nfsrgyd          nfs              7536760      active

  6. Confirm the IP address can be resolved:

    bash-3.2$ host 172.16.105.81
81.105.16.172.in-addr.arpa is  dcol1.delphix.com

    Reference:    IBM AIX: HOW TO SETUP NFSV4 MOUNT IN CLIENT AND SERVER.

AIX resource limit requirements for JDK 17

Before you register an AIX host with Delphix Engine, configure the toolkit-user limits and the per-user process limit as the root user. For an existing host, configure these limits before you run an environment refresh. After you register the host, configure the DB2 instance-user limits before you run dataset enable operations.

Configure the Delphix toolkit user

Replace <Delphix toolkit user> with the operating system user that owns the Delphix toolkit. The environment username and toolkit path are configured when you add the Unix environment. For more information, see Adding a Unix environment.

chsec -f /etc/security/limits -s <Delphix toolkit user> -a data=-1
chsec -f /etc/security/limits -s <Delphix toolkit user> -a data_hard=-1
chsec -f /etc/security/limits -s <Delphix toolkit user> -a nproc=2048
chsec -f /etc/security/limits -s <Delphix toolkit user> -a nproc_hard=4096
chsec -f /etc/security/limits -s <Delphix toolkit user> -a stack=65536
chsec -f /etc/security/limits -s <Delphix toolkit user> -a stack_hard=65536
Configure DB2 instance users

After you register the host, Delphix accesses DB2 instance users through dlpx_db_exec -u <user> during dataset operations. Configure the following limits for every DB2 instance user on the host. To identify these users, go to Manage > Environments > [AIX host] > Environment Users in the Delphix user interface.

Replace <DB2 instance user> with each DB2 instance user.

chsec -f /etc/security/limits -s <DB2 instance user> -a data=-1
chsec -f /etc/security/limits -s <DB2 instance user> -a data_hard=-1
If the data limit is too low for a DB2 instance user, dataset enable operations can hang and fail with a DSP session reset. If the toolkit user's limit is too low, environment refresh or Java validation can fail with a native memory allocation error.
Configure the per-user process limit
chdev -l sys0 -a maxuproc=4096

The maxuproc value sets the per-user process limit and must be at least as high as the toolkit user's nproc_hard value.

Parameter reference

The following values are minimum requirements. Higher process and stack limits are supported.

Parameter Minimum required value Purpose
data / data_hard -1 Sets data and data_hard to unlimited for the toolkit user and every DB2 instance user.
nproc 2048 Provides process and thread capacity for the toolkit user.
nproc_hard 4096 Sets the hard process and thread limit for the toolkit user.
stack / stack_hard 65536 Provides stack capacity for JDK 17 threads.
maxuproc 4096 Sets the per-user process and thread limit.
Verify the settings

Verify the toolkit-user settings:

lssec -f /etc/security/limits -s <Delphix toolkit user> -a data -a data_hard -a nproc -a nproc_hard -a stack -a stack_hard

Log in as the Delphix toolkit user and verify the effective soft and hard limits:

ulimit -a
ulimit -Ha

If the effective limits do not match the values in /etc/security/limits, check the user's .profile and .kshrc files for commands that override the limits. Start a new login session after correcting any overrides.

Verify the settings for each DB2 instance user:

lssec -f /etc/security/limits -s <DB2 instance user> -a data -a data_hard

Log in as each DB2 instance user and verify the effective soft and hard limits:

ulimit -a
ulimit -Ha

Verify the per-user process-limit setting:

lsattr -El sys0 -a maxuproc

A host restart is not required. After you verify the effective limits, retry the environment refresh or dataset enable operation.

Tune the Kernel NFS Client

On AIX, by default the maximum I/O size used for NFS read or write requests is 64K. When Oracle does I/O larger than 64K, the I/O is broken down into smaller requests that are serialized. This may result in poor I/O performance. IBM can provide an Authorized Program Analysis Report (APAR) that allows the I/O size to be configured to a larger value.

  1. Determine the appropriate APAR for the version of AIX you are using:

    AIX Version

    APAR Name

    6.1

    IV24594

    7.1 IV24688

  2. Check if the required APAR is already installed by running the following command. If the APAR is installed, you will see a message similar to this:

    # /usr/sbin/instfix -ik IV24594

  3. If the APAR is not yet installed, you will see a message similar to this:

    All filesets for IV24594 were found.
There was no data for IV24594 in the fix database.

  4. Download and install the APAR as necessary. To find the APARs, perform a search at http://www.ibm.com/us/en/. Specify the name of the APAR you are looking for from step 1. A system reboot is necessary after installing the APAR.

  5. Configure the maximum read and write sizes using the commands below:

    # nfso -p -o nfs_max_read_size=524288
# nfso -p -o nfs_max_write_size=524288

  6. Confirm the correct settings using the command.

    You should see an output similar to this:

    # nfso -L nfs_max_read_size -L nfs_max_write_size  

NAME                CUR   DEF   BOOT  MIN   MAX   UNIT   TYPE  DEPENDENCIES  
--------------------------------------------------------------------------------  
nfs_max_read_size   512K  64K   512K  512   512K  Bytes  D  
--------------------------------------------------------------------------------  
nfs_max_write_size  512K  64K   512K  512   512K  Bytes  D  
--------------------------------------------------------------------------------

OS-specific tuning recommendations for Windows

Receive side scaling

Follow these instructions here to enable RSS: Enable Receive Side Scaling (RSS) on Staging/Target Network Interfaces hosted on the target, such as Oracle, SQL Server, Sybase, or vFiles. They should be applied to all Delphix targets.

Last updated
Oct 9, 2026