interrupt when backup large SQL databases

Backline Root Cause Analysis

RCA Author:

 John Peters

Error Code/Message 

Error 13

Diagnostic Steps 

Verbose logging, TCP dumps, Media,Master,client I/O parameter adjustments

Related E-Tracks

3445293

Problem Description 

 MS SQL backups are failing randomly if MSDP is used.

Cause 

It is believed that several adjustments that have been done on Master and Media Servers  have resolved the issues .  Engineering believes that both Network and IO tuning ended the congestion, hence the bottleneck, resulting NBU to successfully complete backups.

Solution 

 Master, Media Server and client side, I/O parameter adjustments.

Resolution Criteria 

 ----

Description Resolution  (if Criteria is not met) 

In our attempts to determine the root cause of the status 13 failures

when backing up SQL databases to MSDP using media side deduplication,

From the initial logs we could see that after some time, the dbclient

process attempted to send data to the appliance, ie :

16:07:53.335 [17300.26824] <4> VxBSASendData: INF - entering SendData.

16:07:53.335 [17300.26824] <4> dbc_put: INF - sending 65536 bytes

16:07:53.335 [17300.26824] <2> writeToServer: bytesToSend = 65536 bytes

16:07:53.335 [17300.26824] <2> writeToServer: start send -- try=1

16:08:12.224 [17300.26824] <16> writeToServer: ERR - send() to server

on socket failed:

This message occurs a as a consequence of the OS library call send()

returning a non-zero status attempting to send data to a file

descriptor ( socket ) that is associated with a network connection.

When this failure occurs, dbclient sends a failure status to the media

server and bpbrm terminates the job resulting in the status 13. The OS

library call to recv() data on the media server does not receive any

data or indication from other end of the network connection at the time

of the failure which indicates that the TCP stacks on the two hosts are

not in agreement on the state of the connection.

What we needed to find out was if the problem was occurring in the TCP

stack on the client or appliance side of that connection.

In order to understand this, it was felt necessary to look at the

problem from a TCP level, we hoped that this would show if data was

flowing or if there was a plugin ingest issue.

For this to happen, we would need to perform network packet capture

between the hosts, as well as performing strace on bptm  processes

together with full debug logging enabled.

This approach poses a difficult problem based on the intermittent

nature of the failures and the indeterminate time taken for jobs to

fail. The resulting logs would be large and the tcpdump / straces enormous.

We attempted to work around this by rotating the tcp capture logs and

terminating the traces as soon as the job failed in an attempt to

capture the critical information.

However, when we set this test up, the additional load imposed by the

tracing and logging impacted the appliance to such a degree that the

backup eventually failed with a 13, unfortunately we do not feel that

this failure was the same issue seen for earlier failures.

In this case when the job was repeated with tracing turned off it was

successful.

In order to try and prevent the issue occuring we made some

tuning changes to components we felt were potentially the source of the

problem,   specifically :

1) Increased the TCP retransmission settings on the client to 15 (

http://support.microsoft.com/default.aspx?scid=kb;en-us;170359)

2) Implemented following settings on the appliance :

echo 128 > /usr/openv/netbackup/db/config/CD_NUMBER_DATA_BUFFERS

echo 524288 > /usr/openv/netbackup/db/config/CD_SIZE_DATA_BUFFERS

echo 180 > /usr/openv/netbackup/db/config/CD_UPDATE_INTERVAL

touch /usr/openv/netbackup/db/config/CD_WHOLE_IMAGE_COPY

echo 0 > /usr/openv/netbackup/NET_BUFFER_SZ

echo 0 > /usr/openv/netbackup/NET_BUFFER_REST

echo 256 > /usr/openv/netbackup/db/config/NUMBER_DATA_BUFFERS

echo 512 > /usr/openv/netbackup/db/config/NUMBER_DATA_BUFFERS_DISK

echo 16 > /usr/openv/netbackup/db/config/NUMBER_DATA_BUFFERS_FT

echo 1500 > /usr/openv/netbackup/db/config/OS_CD_BUSY_RETRY_LIMIT

echo 262144 > /usr/openv/netbackup/db/config/SIZE_DATA_BUFFERS

echo 1048576 > /usr/openv/netbackup/db/config/SIZE_DATA_BUFFERS_DISK

echo 262144 > /usr/openv/netbackup/db/config/SIZE_DATA_BUFFERS_FT

echo 3600 > /usr/openv/netbackup/db/config/DPS_PROXYDEFAULTRECVTMO

echo 3600 > /usr/openv/netbackup/db/config/DPS_PROXYDEFAULTSENDTMO

touch /usr/openv/netbackup/db/config/DPS_PROXYNOEXPIRE

echo 5000 > /usr/openv/netbackup/db/config/MAX_FILES_PER_ADD

3) Set /usr/openv/pdde/pdcr/etc/contentrouter.cfg

PrefetchThreadNum=16

MaxNumCaches=1024

ReadBufferSize=65536

WorkerThreads=128

4) Set /usr/openv/lib/ost-plugins/pd.conf

PREFETCH_SIZE = 67108864

CR_STATS_TIMER = 300

5) Modified the "Client Communication Buffer size"

Host properties --> Client Settings --> Communication Buffer size set

to 256kb

6) MSSQL script was modified :

BUFFERCOUNT to 2

STRIPE to 4

7) Additionally we would always advise to check the "resolution"

section of this technote http://www.symantec.com/docs/TECH37372.