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

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89
votes
4answers
109k views

FreeBSD performance tuning. Sysctls, loader.conf, kernel

I wanted to share knowledge of tuning FreeBSD via sysctl.conf / loader.conf / KENCONF / etc. It was initially based on Igor Sysoev's (author of nginx) presentation about FreeBSD tuning up to ...
71
votes
4answers
12k views

Why is TCP accept() performance so bad under Xen?

The rate at which my server can accept() new incoming TCP connections is really bad under Xen. The same test on bare metal hardware shows 3-5x speed ups. How come this is so bad under Xen? Can you ...
59
votes
8answers
5k views

How can a single disk in a hardware SATA RAID-10 array bring the entire array to a screeching halt?

Prelude: I'm a code-monkey that's increasingly taken on SysAdmin duties for my small company. My code is our product, and increasingly we provide the same app as SaaS. About 18 months ago I moved ...
55
votes
13answers
10k views

Are networks now faster than disks?

This is a software design question I used to work on the following rule for speed cache memory > memory > disk > network With each step being 5-10 times the previous step (e.g. cache ...
46
votes
8answers
86k views

What limits the maximum number of connections on a Linux server?

What kernel parameter or other settings control the maximum number of TCP sockets that can be open on a Linux server? What are the tradeoffs of allowing more connections? I noticed while load testing ...
40
votes
23answers
58k views

How to copy a large number of files quickly between two servers

I need to transfer a huge amount of mp3s between two serves (Ubuntu). By huge I mean about a million files which are on average 300K. I tried with scp but it would have taken about a week. (about 500 ...
32
votes
7answers
14k views

How much of a performance hit for https vs http for apache?

Roughly how much of a performance hit will https take compared to http for the same page? Suppose I can handle 1000 requests/s for abc.php, how much will it decrease by when accessed through https? I ...
32
votes
5answers
1k views

Pay no attention to that SAN behind the curtain

Once upon a time, I built my own SQL servers, and had control over drive configuration, RAID levels, etc. The traditional advice of separation of data, logs, tempdb, backups, (depending on budget!) ...
31
votes
7answers
59k views

Xen vs KVM in performance

What is faster on same hardware - Xen or KVM? I'm trying to pick-up a virtualization technology to work, which gives the best performance. There are some benchmarks here that I found on the subject: ...
26
votes
9answers
5k views

To improve SQL performance, why not just put lots of RAM rather than having faster hard disks?

People keep telling me that in order to improve an SQL server's performance, buy the fastest hard disks possible with RAID 5, etc. So I was thinking, instead of spending all the money for ...
25
votes
5answers
18k views

Which PHP (opcode) cache one should use and why?

I keep hearing about some PHP (opcode) caches like - APC, XCache, Memcache, eAccelerator, etc. But I couldn't ever figure out how to go about choosing one. Apart from performance benefit, which a ...
24
votes
11answers
18k views

Is virtual machine slower than the underlying physical machine?

This question is quite general, but most specifically I'm interested in knowing if virtual machine running Ubuntu Enterprise Cloud will be any slower than the same physical machine without any ...
24
votes
7answers
10k views

What are the performance differences between Raid 0,1,5,6,10

I have heard/read different performance stories on the various raid flavors. I am curious what the agreed upon best answer is.
21
votes
10answers
17k views

How to make `rm` faster on ext3/linux?

I have ext3 filesystem mounted with default options. On it I have some ~ 100GB files. Removal of any of such files takes long time (8 minutes) and causes a lot of io traffic, which increases load on ...
21
votes
7answers
27k views

How can you know what is w3wp.exe doing? (or how to diagnose a performance problem)

I'm having a performance problem in a site we've made, and I'm not exactly sure how to start diagnosing it. The short description is: We have a very small site (http://hearablog.com) with very little ...
20
votes
5answers
18k views

Can a pool of memcache daemons be used to share sessions more efficiently?

We are moving from a 1 webserver setup to a two webserver setup and I need to start sharing PHP sessions between the two load balanced machines. We already have memcached installed (and started) and ...
20
votes
3answers
6k views

PHP: What are the advantages of FastCGI over mod_php?

It was recently suggested to me that I use FastCGI with PHP. Now I went to the FastCGI page and read it but I don't really understand what the advantages are.
20
votes
7answers
7k views

Is it OK to run perfmon on production servers? And why?

Or should perfmon be limited to a Dev/QA server with load tests that simulate production activity? I'd like to run perfmon for two days (like Sql Server master Brent Ozar suggests) to get an overall ...
19
votes
4answers
1k views

Why would a heavily disk intensive application run faster on a SAN than on a Physical Disk?

Why would a heavily disk intensive application run faster on a SAN than on a Physical Disk? I would have expected the Physical disk to be slightly faster but in fact the process ran 100 times faster ...
19
votes
8answers
18k views

What impact does full hard drive encryption have on performance?

We have HP notebooks here at work, and it is policy to have HP's hard drive encryption turned on to protect client databases and IP in the case of loss/theft. I was wondering if there was any ...
18
votes
5answers
1k views

Extremely fast booting server

I'm changing the way that our DHCP/DNS stuff works at work. Currently we've got 3 DNS servers, and a DHCP box. All of them are VMs. There's a circular dependency where stuff booting requires NFS, ...
18
votes
3answers
38k views

Optimal values for ServerLimit, MaxClients, MaxRequestsPerChild directives

I'm running a traffic intense site plenty of dynamic content, mostly user-generated. The server is a dedicated one and has a total of 4 Intel(R) Xeon(R) CPU X3210 @ 2.13GHz proccesors. I need to know ...
18
votes
8answers
8k views

Analyzing Linux NFS server performance

I'd like to do some analysis of our NFS server to help track down potential bottlenecks in our applications. The server is running SUSE Enterprise Linux 10. The kind of things I'm looking to know ...
17
votes
2answers
1k views

Can a virtualized machine have the CPU and RAM resources of multiple underlying physical machines?

We are studying implementing some virtualized servers here, but we don't know what will be better suitable for us. Some folks are saying better have two huge servers, and others are saying have like a ...
17
votes
3answers
17k views

Why is my rsync so slow?

My Laptop and my workstation are both connected to a Gigabit Switch. Both are running Linux. But when I copy files with rsync, it performs badly. I get about 22 MB/s. Shouldn't I theoretically get ...
16
votes
17answers
18k views

What network file sharing protocol has the best performance and reliability?

We have a setup with a few web servers being load-balanced. We want to have some sort of network shared storage that all of the web servers can access. It will be used as a place to store files ...
16
votes
4answers
14k views

How to pick between RabbitMQ and ZeroMQ or something else?

I'm looking for a queuing system which is fast and reliable and potentially can be spread across machines. Platform is Linux. Open source is preferable. Both RabbitMQ and ZeroMQ look good but I ...
16
votes
10answers
15k views

How do I profile MySQL?

What tools exist to profile MySQL, like how MSSQL 2000+ does with the SQL Profiler? I'd want to trace things like SQL statements executed, execution times, execution plan, etc.
15
votes
4answers
1k views

HTTP Compression on IIS 6.0 (Windows Server 2003)

There are many things you have to do/consider when you want to enable HTTP compression on IIS 6.0 (Windows Server 2003). Can somebody please provide a comprehensive list of the actions you have to ...
15
votes
5answers
26k views

How many Context Switches is “normal” (as a function of CPU cores (or other))?

Do any of you have a rule of thumb as to how many context switches (per processor core) is Normal on a Linux server? My college here brought it up, and he's seeing 16K on a 8-core x86_64 machine. ...
15
votes
4answers
3k views

Apache or NGINX for PHP?

I've read quite a bit on the major benefits to running NGINX over Apache for serving static files. However, I have never seen an article talking about Apache vs NGINX for serving PHP pages. Question: ...
14
votes
10answers
3k views

Would rebooting the server in a schedule be good idea for performance?

I am wondering if rebooting a server in a schedule would be good idea for performance. Let's say we want to reboot the server at 02:00 AM per 2 nights. The server here is Windows Server 2008 R2. ...
14
votes
11answers
14k views

What can cause slow ssh session? [closed]

I ssh on remote host but terminal performance is poor. Symbols I am typing are not shown immediately, but with some delay. Sometimes two symbols are shown at one time after delay.
14
votes
4answers
942 views

How do limit disc i/o during backup?

I have a cron that basically do a simple "tar zcf" in the night. The server has: 8 Cores - Intel(R) Xeon(R) CPU E5606 @ 2.13GHz 25GB RAM Ubuntu 12.04.2 LTS Hardware RAID 1 (LSI Logic / Symbios ...
14
votes
7answers
11k views

What is the best filesystem for insert performance on PostgreSQL?

I'm curious if anyone out there has done any experimentation or comparisons between file systems and database performance. On Linux, I'm wondering what is the optimal file system for a postgres ...
14
votes
1answer
16k views

Determining which process is causing heavy disk I/O?

I've seen this question: How to identify heavy write to disk? And I've used dstat and atop before...but they don't seem to pinpoint what process is causing disk I/O. For example, from dstat: dstat ...
14
votes
6answers
497 views

First days online : how not to kill your site

Suppose you have this fancy new site, with lots of data (like big images), and you're about to put it online. If you do "too much" publicity, during the first days, the site will be overwhelmed with ...
14
votes
16answers
9k views

Real time monitoring of MS Windows servers and their services

We have a bunch of large HDTVs in our monitoring office keeping an eye on all of our production equipment. We are monitoring: Cisco routers HP switches HP proliant servers Windows 2003 IIS SQL ...
14
votes
3answers
536 views

Does this prove a network bandwidth bottleneck?

I've incorrectly assumed that my internal AB testing means my server can handle 1k concurrency @3k hits per second. My theory at at the moment is that the network is the bottleneck. The server can't ...
14
votes
2answers
11k views

limit linux background flush (dirty pages)

Background flushing in linux happens when either too much written data is pending (adjustable via /proc/sys/vm/dirty_background_ratio) or a timeout for pending writes is reached ...
14
votes
3answers
12k views

GlusterFS vs Ceph, which is better for production use for the moment? [closed]

I am evaluating GlusterFS and Ceph, seems Gluster is FUSE based which means it may be not as fast as Ceph. But looks like Gluster got a very friendly control panel and is ease to use. Ceph was ...
13
votes
8answers
5k views

Doing an rm -rf on a massive directory tree takes hours

We're using rsnapshot for backups. It keeps lots of snapshots of the backuped up file, but it does delete old ones. This is good. However it's taking about 7 hours to do a rm -rf on a massive ...
13
votes
10answers
6k views

System degredation - does Windows slow down over time?

I am having a small squabble at work with our admin regarding a colleague's laptop. The laptop is bordering on unusable. The admin tidied up some temp directories and defragged the HDD a few months ...
13
votes
5answers
990 views

Which bots and spiders should I block in robots.txt?

In order to: Increase security of my website Reduce bandwidth requirements Prevent email address harvesting
13
votes
1answer
4k views

Apache 2.2 mpm_worker: more threads or more processes?

When using the Worker MPM in Apache, you can fiddle with the number of child processes and the number of server threads per child process. What are the advantages and disadvantages of each? Under ...
13
votes
3answers
2k views

Some Linux systems become very slow when Redis is loading a big dataset

I received a report from a Redis user, and I'm not sure what to reply as I'm not an expert in the area of Linux and its scheduler, however we (as the Redis project) need to figure this kind of issues ...
12
votes
11answers
7k views

Should I run my database off of a RAID 5 configuration?

I've heard that the write performance of RAID 5 can be appalling at times. While I want the redundancy that it provides I don't want to sacrifice my database insert/update times. Is this something I ...
12
votes
4answers
2k views

Why is 1 of my 24 CPUs Pegged at 100%?

I have an HP ProLiant DL380 G7 system using 2 6-core CPUs, with Hyper-threading enabled, for a total of 24 logical CPUs (as seen by Windows). When running our application, total system CPU ...
12
votes
2answers
398 views

Performance impact of running different filesystems on a single Linux server

The book "HBase: The definitive guide" states that Installing different filesystems on a single server is not recommended. This can have adverse effects on performance as the kernel may have to ...
12
votes
3answers
4k views

OpenVPN performance: how many concurrent clients are possible?

I am evaluating a system for a client where many OpenVPN clients connect to a OpenVPN server. "Many" means 50000 - 1000000. Why do I do that? The clients are distributed embedded systems, each ...