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

learn more… | top users | synonyms (2)

7
votes
5answers
7k views

Linux md vs. LVM performance

I am trying to tune my NAS, running openfiler, and wondering why I'm getting relatively poor read performance from 4 WD RE3 drives in RAID 5. EDIT: Please note I am talking about the buffered disk ...
7
votes
4answers
3k views

Experience in migrating from Apache to nginx?

I'd like to get some feedback about a migration From Apache to nginx. My goal is to reduce the memory footprint of the web server. Currently, I use the following modules.features on Apache: multiple ...
7
votes
7answers
6k views

Windows Server 2008 R2 grinds to a screeching halt during file copy operations

When my Windows Server 2008 R2 machine is performing any large disk operations (copying 10GB files from one drive to another, copying similar file over network, merging HyperV snapshots, compressing ...
7
votes
5answers
6k views

FreeBSD jails vs virtualization performance

I'll soon buy myself a nice server (something like the quad-cpu HP DL585) for personal use (home related stuff, data-mining projects, web server and some cron jobs), and I wonder how to separate all ...
7
votes
1answer
65 views

What do users see when Apache reaches MaxClients?

Occasionally, in my Apache error log, I will find: [error] server reached MaxClients setting, consider raising the MaxClients setting I've purposely lowered MaxClients in the past (to 60) due to ...
7
votes
2answers
416 views

Can I have 2Gbit over 1Gbit Nics [closed]

So this really baffles me. Apparently because 1Gbit can transmit data in both directions simultaneously it should be possible to get 2Gbit of data transfer on a single NIC (1Gbit flow seend and 1Gbit ...
7
votes
3answers
361 views

Can gigabit media converters affect performance?

We are looking to upgrade our network infrastructure. We have fiber between our IDFs and our MDF but have found fiber core switches to be significantly more expensive than copper. If we were to have a ...
7
votes
1answer
347 views

SQL Server 2005 Performance Audit

Do you guys have any good step by step type links for performing an SQL Server 2005 Performance Audit? Something like this link would be great but for SQL Server 2005.
7
votes
1answer
1k views

KVM/Qemu, Ubuntu: Why do more guests CPUs enhance Disk-I/O rapidly?

We have an Heartbeat/DRBD/Pacemaker/KVM/Qemu/libvirt cluster consisting of two nodes. Each node runs Ubuntu 12.04 64 Bit with the following packages/versions: Kernel 3.2.0-32-generic #51-Ubuntu SMP ...
7
votes
1answer
2k views

Best practices for choosing fs block size on ext3/4?

I never really pay block size much attention but obviously there can be benefits to choosing something other than the default. I am looking for a good "best practices" paper on choosing block size. ...
7
votes
5answers
565 views

ASP.NET High CPU Bringing Servers to their Knees

Ok, our new build is having 100% cpu spikes on each server at random intervals. For long durations it make the site totally unresponsive - this will be at peak times as people in different countries ...
7
votes
3answers
6k 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
1answer
261 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
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
5answers
6k 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
2answers
661 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
1answer
2k views

At what point is EBS usage the bottleneck?

I've got a site hosted on Amazon using a EC2 instance backed by an EBS volume. On the weekends, traffic spikes and I make the instance larger which helps quite a bit -- I'm no longer seeing CPU usage ...
7
votes
3answers
684 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
6answers
5k views

Is there a point in using Prelink anymore?

Over the years using various linux boxes, I've gotten into the habbit of using prelink ritually to accelerate load times of applications. However, the benefits of running prelink are negated every ...
7
votes
1answer
3k 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
2answers
478 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
339 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
391 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 ...
6
votes
9answers
5k views

Linux: How to find out whether the harddrive is causing a bottleneck?

I'm not asking how to find out where a bottleneck is. I just what to know how to check if the harddrive is being used at its limit (and hence causing a bottleneck). Something like top where I can see ...
6
votes
8answers
3k 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
9answers
3k 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
3k views

Monitor system CPU / system calls in Linux

I have a couple processes that are eating up a lot of system CPU time (as determined by looking at vmstat). Is there an easy way to find out what kind of system calls are being made? I know there ...
6
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
3answers
9k views

What KVM disk type to use?

I'm setting up a few KVM virtual guests and I'm debating which disk type to use. I haven't been able to find a good resource online that runs down the pros and cons of each. Can you help me create a ...
6
votes
4answers
1k 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
7answers
10k views

Slow NFS transfer performance of small files

I'm using Openfiler 2.3 on an HP ML370 G5, Smart Array P400, SAS disks combined using RAID 1+0. I set up an NFS share from ext3 partition using Openfiler's web based configuration, and I succeeded to ...
6
votes
5answers
4k views

How to measure disk throughput?

I want to know how many bytes per second can I write to the disk and read from it. How can I do that on linux machine?
6
votes
2answers
2k views

How do you disable the “last accessed” attribute on NTFS/Windows?

Inspired by this answer, I realize I have no idea how to disable the last accessed attribute in Windows to increase performance. If you can, how? I know in Linux you can mount the partition with the ...
6
votes
4answers
576 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
2k 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
12k 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
1answer
136 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
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
163 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
3answers
26k views

How to set shmall, shmmax, shmni, etc … in general and for postgresql

I've used the documentation from PostgreSQL to set it for example this config: >>> cat /proc/meminfo MemTotal: 16345480 kB MemFree: 1770128 kB Buffers: 382184 kB ...
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 ...
6
votes
4answers
8k views

How can I find out what is causing interrupts on Windows?

Occasionally I come across servers (Windows 2003 and 2008) with high processor % interrupt time. Is there a way to see what program or device is causing the interrupts?
6
votes
6answers
8k views

How many files in a directory is too many? (Downloading data from net)

Greetings, I'm writing some scripts to process images from various photo websites. Right now I'm storing all this data in individual text files in the same directory. The directory is web ...
6
votes
2answers
1k views

Importance of disk alignment for Windows Server 2012

I saw article about Disk alignment here and also here.Also there where some references that windows server 2003 has some problem with disk alignment. After reading article I am confused whether we ...
6
votes
3answers
229 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
1answer
7k 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
1answer
64 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
175 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. ...
6
votes
2answers
787 views

Why is Postgres sitting 95% idle, with no file I/O?

I have a TileMill/PostGIS stack running on an 8 core Ubuntu 12.04 VM on an OpenStack cloud. It's a rebuild of a very similar system which was running nicely on very similar hardware (same cloud, but ...
6
votes
1answer
4k views

Nginx auto minify html output

does anyone know of a way to get nginx (or any other method) to minify html output on the fly? It seems straightforward to me and can shave a few kb off and help speed up the site.