Our Unixadmin, John from xyz company,  recently upgraded one of his server’s network interface card  from the old one with 100MB speed to a new one with 10Gig speed , and the reason is to improve the speed for the backup of the server. After the NIC Upgrade  john found that the server network performance was improved a little, but still the server is not able to utilize all the available network bandwidth. 

After a bit of investigation john realised that his server TCP window size has to be tuned  to utilize maximum network bandwidth available to the server.  In this post we will be discussing the procedure about “how john tuned the TCP window size  to increase his server network performance?”.

  Full Story

Memory bottlenecks are evidenced by two different things happening on the system — paging and swapping. Paging refers to pages of memory being reclaimed by the page daemon when the system starts to get low on free memory. Swapping is more extreme, and refers to entire processes being swapped out.

To determine if you are only paging, or also swapping, examine two columns in the vmstat output. The first column is the sr column. If the value in this column is greater than zero then the page scanner is scanning memory pages to put them back on the free list to be reused.

The page scanner runs when memory falls under the value of a system parameter known as lostfree – default value is 1/64th of physical memory – or cachefree if priority_paging is enabled default value is 1/128th of physical memory.

You should not worry about high scan rates if you are using the file system heavily. High scan rates can be normal in many circumstances. If priority_paging is enable, the page scanner steals the pages more effectively so the file system I/O does not cause unnecessary paging of applications. priority_paging causes sr rate to be higher for its own good. Solaris 8 introduces the cyclic cache. With cyclic cache, the scanner is not used to reclaim pages during file system I/O therefore if sr is greater than 0 then it’s a indication that the system is running low in memory.

Full Story

This post is to highlight some of the steps needed to diagnose if an issue is in fact a disk performance issue or not.  And if it is, what data will be collected to help diagnose the issue. Please note that performance in general is not an easy issue to tackle.  This is because it can be caused by many issues that may not be disk related. Full Story

Collisions may occour on ethernet links which are operating at Half Duplex (HDX). They do not occour on links using Full Duplex (FDX). The normal formula to calculate the packet collision rate is:

( collisions / output packets ) * 100 = collision rate

For example:

# netstat -i 10

input   lo0:1     output           input  (Total)    output
packets errs  packets errs  colls  packets errs  packets errs  colls
135299  1     19240   0     691    135910  1     19851   0     691

# bc -l

691/19240 * 100 <RETURN>
3.59147609147609147600 (= 3.59 % collision rate)

The following rough guidelines are common among network administrators.

• Collision rates < 5% are considered ok.
• Collision rates > 5% are the first indication of possible network loading
• Collision rates > 10% may signify an over-loaded network.

It is important to note that the collision rate:

1. of a given machine does not represent the average for the entire network,
2. threshold varies greatly, and
3. it is not an indication of actual load on the network (Collisions + Defers).

NOTE 1 : When looking at a systems collisions compared to output packets it is important to note that this is only one node’s perspective of the network while it is transmitting.

NOTE 2 : Depending on the applications running and protocol used, a high collision rate (>50%) may not cause a decrease in perceived throughput on a client, but a server may show performance degradation at 5-10%.

NOTE 3 : It is recommended to use a Network Sniffer/Analyzer to get a overall network analysis and better identify the problem.

NOTE 4 : Segmentation and/or the use of ethernet switches is normally the solution to a network-wide collision and netload issue.





Full Story

First you’ll need to check  how much Memory is used in Kernel and how much is used in User Memory. This is important to decide, what troubleshooting steps are required.
A nice mdb dcmd ( this command can take several minutes to complete, and you have to be extremely careful to run this command ) Solaris 9 Operating System or greater only !

# echo “::memstat” | mdb -k
Page Summary      Pages                 MB          %Tot
———— —————- —————-  —-
Kernel              151528              1183            10%
Anon                185037              1445            12%
Exec and libs      17092                133              1%
Page cache       281433              2198            19%
Free (cachelist) 633893              4952            42%
Free (freelist)    235470              1839            16%
Total               1504453            11753

  Full Story

This Video presents you the procedure to investigate various  performance bottlenecks related to Memory, CPU and IO  using the commands iostat, vmstat and prstat.