Questions about server hardware and software performance, or network performance.

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7
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2answers
3k views

Too much I/O generated by postgres stats collector process

I am using XenServer with several virtual machines having local postgres databases. Even when all applications are unused and the databases are idle, each vm causes constant storage network traffic ...
7
votes
3answers
4k views

PostgreSQL slow commit performance

We are having some problems with a PostgreSQL configuration. After some benchmarks I found out that very simple queries are taking a relatively long time, upon furter inspection it appears that the ...
7
votes
2answers
1k views

Linux disable disk cache for a single command

Our server is performing decently, but when backups or other scan processes run it will tank the entire server. Something like clamd will run and scan many files. While we expect slow performance, it'...
7
votes
3answers
7k views

TIME_WAIT connections not being cleaned up after timeout period expires

I am stress testing one of my servers by hitting it with a constant stream of new network connections, the tcp_fin_timeout is set to 60, so if I send a constant stream of something like 100 requests ...
7
votes
5answers
8k views

How can I replay Apache access logs back at my servers to do real world load testing?

I looked at http://serverfault.com/questions/2107/tools-for-load-testing-http-servers but I couldn't see how to replay my own existing logs in any of those tools. I have a bug that only occurs under ...
7
votes
1answer
376 views

virtual disk image - file or partition

I'm looking at the differences between using a file versus a partition to store a virtual disk image in VM use. The common knowledge is that partition-based images are faster than file-based images ...
7
votes
4answers
3k views

better TCP performance over a “high delay network”

I’m trying to improve my TCP throughput over a “high delay network” between Linux machines. I set tcp_mem, tcp_wmem and tcp_rmem to “8192 7061504 7061504”. I set rmem_max, wmem_max, rmem_default and ...
7
votes
1answer
3k views

How to select the best Stripe Size when configuring a RAID Array

There are various "references" on the Internet that delve into some discussion about what factors to consider when selecting a particular RAID stripe size (4KB to 128KB or more) for an array of disks, ...
7
votes
1answer
1k views

ext3 file system performance tuning: what metrics to monitor

I have a high-IO application that is working, and scaling well to date. Over the past few months we've been trying to look down the road and predict where our next bottlenecks will occur. One of ...
7
votes
2answers
9k views

Relation between disk IOPS and sar tps

I'm trying to estimate IOPS requirements of my application running on 32-bit CentOS 6.2. I started to take some measurement on a machine with SATA disks and I'm quite confused of difference between ...
7
votes
2answers
816 views

Does speed of ZFS snapshot rollback depend on number of files?

I have tested a 10Gbit connection between two hosts to be able to read a 10GB file from host1 and write it to host2 using netcat, where the speed was 410MB/s. When I ZFS send/receive again with ...
7
votes
3answers
882 views

Why is there less latency on loopback than on a carp interface?

Stack Overflow Careers is served up something like so: user -> internet -> our fw -> nginx -> haproxy -> web farm FreeBSD is the operating system in use no firewalling or QoS is in ...
7
votes
1answer
4k views

Why the performance decrease for an SSD when using Hyper-V?

I've just installed my new M4 256GB on a Windows Server 2008 R2 Hyper-V server. On the host system using Crystal Disk Mark I've got 212 Mb/s as 4k QD32 write performance, but when I create a VHD disk ...
7
votes
1answer
2k views

windws server 2008 udp multicast performance problem

I encounter a strange performance problem on 2008 R2 Enterprise SP1. Here is the setup: Many processes listening to distinct Multicast UDP streams (5 multicasts listen by process) bound on a single ...
7
votes
1answer
211 views

Extreme ZFS slowdowns after several months

I've got a general-purpose server, providing mail, DNS, web, databases, and some other services for a number of users. It's got a Xeon E3-1275 at 3.40 GHz, 16 GB ECC RAM. Running Linux kernel 4.2.3, ...
7
votes
2answers
537 views

Network performance deteriorates when uninvolved device on switch is shut down

I am witnessing very counter-intuitive effect in my network setup. I have a network setup with three devices (let's call them server, laptop and nettop, all running Linux, details below) connected to ...
7
votes
1answer
363 views

RAID with 4 drives offers very minimal speed improvement

Setup 1.5TB x 8 on a SANS Digital enclosure configured into two sets of 4 drives and connected to a Windows Server 2003 computer over eSATA. They are all identical Seagate Barracuda ST31500341AS ...
7
votes
1answer
503 views

sys.dm_exec_query_stats interaction with recompilation

We use sys.dm_exec_query_stats to track down slow queries and queries that are IO offenders. This works great, we get a lot of very insightful stats. It is clear this is not as accurate as running a ...
7
votes
1answer
121 views

Sluggish performance on NTFS drive with large number of files

I am looking at this setup: Windows Server 2012 1 TB NTFS drive, 4 KB clusters, ~90% full ~10M files stored in 10,000 folders = ~1,000 files/folder Files mostly quite small < 50 KB Virtual drive ...
6
votes
3answers
10k views

Understanding RedHat's recommended tuned profiles

We are going to roll out tuned (and numad) on ~1000 servers, the majority of them being VMware servers either on NetApp or 3Par storage. According to RedHats documentation we should choose the ...
6
votes
8answers
4k views

SQL Server slow in production environment

I have a weird problem in a customer's production environment. I can't give any details on the infrastructure, except that SQL server runs on a virtual server. The data, log and filestream file are on ...
6
votes
4answers
12k views

How do I configure RAID 5, especially stripe size, with 24 x 1.2 TB drives for CentOS 6?

For a Dell R920 with 24 x 1.2TB disks (and 1TB RAM), I'm looking to set up a RAID 5 configuration for fast IO. The server will be used to host KVM VMs that will be reading/writing files of all sizes, ...
6
votes
3answers
6k views

How can I find out where a file is physically located on the disk (block numbers)?

This is an obscure question, I know. I'm trying to do some performance testing of some disks on a Linux box. I'm getting some inconsistent results, running the same test on the same disk. I know ...
6
votes
9answers
4k views

Linux Server Performance Monitoring

I'm looking to monitor performance on my Linux servers (which happen to be Centos). What are the best tools for monitoring things in realtime such as: Disk Performance I/O, swapping etc.. CPU ...
6
votes
3answers
35k views

HDD: performance differences between 7.2k SATA and 15k SAS

What is the rule of thumb in performance characteristics and differences between 7200rpm (SATA/SAS) and 15000rpm (SAS) hard disc drives of the same generation?
6
votes
2answers
6k views

In absense of iotop which command is most appropriate for get i/o bounded process

Suggest me best way to list io bounded process. I know iotop is best way to get list but want any alternate option since my system showing a large number of D state process.
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votes
6answers
7k views

Find the bottleneck: disk I/O on Windows XP

One of our development boxes has developed a problem wherein performance will occasionally drop through the floor. When this happens, you can hear the hard drive thrashing, but I don't know what's ...
6
votes
4answers
2k views

Will a database server perform better running on 2 CPUs with 16 cores or 4 CPUs with 8 cores?

What I have: an online financial application (ASP.NET, C#) at peak we have 5K+ simultaneous users backend is running on Oracle 11g (active server + stand-by using Active Data Guard). At peak - 4K-5K ...
6
votes
4answers
7k views

Nagios remote monitoring: NRPE Vs. SSH

We use Nagios to monitor quite a few (~130) servers. We monitor CPU, Disk, RAM and a few other things on each server. I've always used SSH to run the remote commands, purely because it requires little ...
6
votes
3answers
9k views

mkfs Operation Takes Very Long on Linux Software Raid 5

I've set-up a Linux software raid level 5 consisting of 4 * 2 TB disks. The disk array was created with a 64k stripe size and no other configuration parameters. After the initial rebuild I tried to ...
6
votes
2answers
3k views

ZFS with L2ARC (SSD) slower for random seeks than without L2ARC

I am currently testing ZFS (Opensolaris 2009.06) in an older fileserver to evaluate its use for our needs. Our current setup is as follows: Dual core (2,4 GHz) with 4 GB RAM 3x SATA controller with ...
6
votes
4answers
15k views

MS SQL server: Single or multiple instances?

How costly (CPU or memory wise) is it to have multiple instances of SQL server 2005 instead of only one instance with prefixed databases? A company have three application providers. They each will ...
6
votes
1answer
1k views

Is it bad practice to run a web application server directly on port 80/443

I am hosting a web app on amazon aws, using an ec2 instance. On that instance i will be running only one application. using glassfish v3.0.1 I do not want to run the app using : www.mydomain.com:...
6
votes
4answers
599 views

Suggestions for recommended file system for Linux server

There are many file systems for a Linux server administrator to choose from. Also, it is not always an easy task to figure out the appropriate layout and optimal file system for your needs. Can you ...
6
votes
2answers
3k views

Why does apache slow down overnight?

Greetings experts, On my dedicated CentOS 5.4 server, I configure apache with about a dozen virtual hosts. I test a few of 'em, each loads within about a second; fairly quick. Load average is less ...
6
votes
6answers
13k views

How to troubleshoot slow Windows XP boot?

I have a Windows XP x64 SP2 machine that used to boot up really quickly, but now takes a very long time. If I enable the /sos boot switch it gets to the bit where it says: 2 system processors [8191MB ...
6
votes
2answers
3k views

does adding heaps of drives to a raid 0 increase performance?

does adding heaps of drives to a raid 0 increase performance? i know that two drives in a striped raid will usually be faster than a single drive but will i notice a difference in performance between ...
6
votes
1answer
151 views

How to prevent IO Load under Linux for Video serving?

I'm currently serving videos of conferences via Nginx on 3 servers; 4 cores, enough memory (no swap used) and RAID-10 with 8 drives per server. Unfortunately iostat -xd 1 gives me 100% on all 3 ...
6
votes
1answer
11k views

How is memcache distributed?

I've got memcache running on 5 web servers all of which are on the host list in php and which are load balanced on the front end. So since memcached is supposed to be distributed the php client will ...
6
votes
3answers
10k views

Configuring Varnish to rewrite Expires/Cache-Control headers for client-side caching

How do I configure Varnish so that all responses to requests matching say "*.css" gets cached in the client's browser for 30 days? What I'm trying to achieve is making Varnish set the correct "...
6
votes
3answers
3k views

Best Linux network tuning tips? [closed]

I figure it's a good idea to have a central question for linux network tuning. I'm particularly interested in tuning options for the following. Web server Varnish / Squid server DB server File ...
6
votes
2answers
180 views

What Linux command do I type to see my MySQL server load in real time?

What Linux command can I type where I can watch MySQL server load in real time? BACKGROUND: I can type 'top' and watch overall server load (just look at inverse of Idle % and consider it over a ...
6
votes
6answers
3k views

Windows 2008 Server on mixed ethernet speeds — download from share slow, but fast plain TCP

I have a Windows Server 2008 R2 x64 server that is AD controller and file server. I have a problem that Windows XP clients experience terribly slow (less than 10Mbps, really less than ten-megabits-per-...
6
votes
2answers
13k views

Why do MySQL queries pile up in “Sending data” state?

We're using InnoDB tables as the back end of a web application, and everything was fine for about two years until we had to restart MySQL a few weeks ago. (We hadn't disabled reverse DNS lookups, ...
6
votes
1answer
361 views

4X10GB Bonded NIC - only producing 4-5GB throughput

I have Two HPBL685c G6 blade servers running Ubuntu 15.04 Each server has 4X10GB NIC 2x10GB NIC are connected to a single VirtualConnect 10/10G Ethernet module The other 2x10GB NIC are connected to ...
6
votes
2answers
9k views

jbd2/dm-0-8 consuming all I/O

What is jbd2/dm-0-8 and why It is consuming all my I/O usage and causing I/O wait? Is there anyway to disable this? Bonnie++ results: http://pastebin.com/iQCWP1qp $ sudo hdparm -t /dev/sda1 /dev/...
6
votes
3answers
241 views

PHP + MYSQL site perfomance

I have to manage a site which wasn't developed by me. It is in PHP using a mysql database, which is located in the web server. The site, sometimes (when the visitors increase too much) stops ...
6
votes
3answers
4k views

Apache + Tomcat VS Stand Alone Tomcat or GlassFish

I am setting up a Debian server to serve Java web applications. I have done quite a bit of research for several weeks now. Tomcat's web site says it is better to use stand alone Tomcat for speed if ...
6
votes
1answer
111 views

postfix performance with lists in main.cf

For defining a list of items to assign to many different options in postfix, you can either use a comma separated list like this: relay_domains = example.com,example.net,example.org or a hash map ...
6
votes
2answers
283 views

Calling sync/fsync slows IO after 30 minutes uptime

After 30 minutes of uptime using Ubuntu 14.04 with an ext4 hybrid SSD I see many processes blocking IO using iotop. The root cause of this slowdown has been traced back to the Unix system call sync. ...