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

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12
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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
7answers
759 views

How do storage IOPS change in response to disk capacity?

All other things being equal, how would a storage array's IOPS performance change if one used larger disks. For example, take an array with 10 X 100GB disks. Measure IOPS for sequential 256kb block ...
12
votes
4answers
4k views

Ubuntu's garbage collection cron job for PHP sessions takes 25 minutes to run, why?

Ubuntu has a cron job set up which looks for and deletes old PHP sessions: # Look for and purge old sessions every 30 minutes 09,39 * * * * root [ -x /usr/lib/php5/maxlifetime ] \ ...
12
votes
2answers
412 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
10answers
7k views

How to scale php5+MySQL above 200 requests/second?

I am tweaking my homepage for performance, currently it handles about 200 requests/second on 3.14.by which eats 6 SQL queries, and 20 req/second on 3.14.by/forum which is phpBB forum. Strangely ...
12
votes
3answers
3k views

How fast is MySQL replication?

I'm considering setting up replication of our mysql db to be able to have local slaves in each of our branch offices, while having the master in the main office to improve application performance ...
12
votes
6answers
17k views

How can I disable encryption on openssh?

I'm having performance problems using openshh(server) and putty(client) combination to use a remote webproxy. I'd like to disable encryption and test the results to see if it makes a difference. How ...
12
votes
1answer
16k views

Why is my rsync so slow compared to pure cp or even scp?

I'm transfering the files from Linux to Windows 7 via a mounted share (the share is mounted from Windows on Linux).. I'm copying lots of data (i.e. nearly a TB) from the old to the new machine within ...
12
votes
9answers
1k views

When to move a virtualized server to physical?

Virtualization has some great benefits, but there are times when a virtualized server needs more performance and should be moved to physical. My question is, how do you tell when these times are? I'm ...
12
votes
4answers
468 views

How to best tune a Windows development machine?

How to best tune a Windows PC for development purposes?
12
votes
3answers
3k views

MySQL Replication Performance

I'm having a serious issue with MySQL 5.5 replication performance between two machines, mostly myISAM tables with statement based replication. The binary logs and mysql data directory are both located ...
12
votes
1answer
741 views

Apache performance degrades dramatically above ~256 simultaneous requests

I'm running a relatively low-traffic site that experiences a large spike in visitors once a week following a site update. During this spike, site performance is extremely poor compared to the rest of ...
12
votes
1answer
751 views

Why do we get a sudden spike in response times?

We have an API that is implemented using ServiceStack which is hosted in IIS. While performing load testing of the API we discovered that the response times are good but that they deteriorate rapidly ...
12
votes
4answers
564 views

IIS7 ASP.NET application - 2 identical apps in 2 identical app pools, 1 is responsive and 1 is not

I have an ASP.NET (v4.0) web app that is installed in a virtual directory (as an application) and is hosted in it's own app pool. This is repeated for each instance of the app (i.e. per customer). ...
11
votes
4answers
3k 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 ...
11
votes
13answers
9k views

Why would wireless routers become less reliable over time?

I've been curious about this for awhile now. I don't know if I'm seeing a real pattern or not, but having worked with many home office/small office wireless routers for a few years now, I've noticed ...
11
votes
3answers
5k views

Do you use performance counters on production IIS web sites?

Do you keep the counter ON during heavy production loads Which performance counters do you find useful for ASP.Net/IIS 6.0 websites?
11
votes
11answers
13k views

A monitoring tool that captures processes' memory usage/cpu usage, etc over time

I am looking for a way to diagnose issues, such as swap death, where a balooning memory process fills up swap and kills the whole machine (such as apache). I'm already using cacti and I can set up ...
11
votes
10answers
4k views

Are there any good reasons for disabling hardware-assisted virtualization?

We've had a number of servers from Dell recently, all of which have had hardware-assisted virtualization disabled in the BIOS. As far as I know hardware-assisted virtualization is a good thing - so ...
11
votes
1answer
385 views

ext4 listing of files very slow in one specific directory that contained lots of files before

Background I had a small logrotate misshap... Logrotate would rotate the archived logs by misstake causing a quadratic growth of files in my /var/log/. And by the time I caught wind that something ...
11
votes
2answers
12k views

Best Mysql cache settings for 8gb RAM dedicated mysql server using only Innodb (5gb database)

I'm a pretty big noob when it comes to setting up mysql for performance. And honestly I'm not worried about the fine tuning to squeeze every last bit of performance out of mysql, but I do know that ...
11
votes
7answers
10k views

Troubleshooting a “slow” network

We've all had a complaint that the "network" is "slow" at some point: might be localized to one room (switch) or one computer, might just be Internet (DNS? Browser issue?), might be just one ...
11
votes
4answers
5k views

Why VM snapshots are affecting performance?

I read in one of the VMware KB article says that snapshots will directly proportional to VM performance. But my team keep asking me how snapshots can affect performance. I would like to give them ...
11
votes
3answers
6k views

How much overhead does x86/x64 virtualization have?

How much overhead does x86/x64 virtualization (I'll probably be using VirtualBox, possbly VMWare, definitely not paravirtualization) have for each of the following operations a Win64 host and Linux64 ...
11
votes
3answers
1k views

Determining a realistic measure of requests per second for a web server

I'm setting up a nginx stack and optimizing the configuration before going live. Running ab to stress test the machine, I was disappointed to see things topping out at 150 requests per second with a ...
10
votes
8answers
8k views

Should I completely turn off swap for linux webserver?

Recently my friend told me that it is a good idea to turn off swap on linux webservers with enough memory. My server has 12 GB and currently uses 4GB (not counting cache and buffers) under peak load. ...
10
votes
4answers
1k views

Why HDD rotate at 7200 rpm?

I was wondering why hard drives rotate at these specific speed (5400,7200, ...) and not other values.
10
votes
10answers
767 views

How does the number of subdirectories impact drive read / write performance on Linux?

I've got an EXT3 formatted drive on a Linux CentOS server. This is a web app data drive and contains a directory for every user account ( there are 25,000 users ). Each folder contains files that ...
10
votes
8answers
4k views

Best file system for external (USB) hard drives/USB memory media

Almost all external USB hard drive and USB memory media/sticks come today preformatted with FAT32. As far as I know the only advantage of the file system is the compatibility among OSes and devices. ...
10
votes
3answers
11k views

Why is Apache running so many processes? Excessive RAM here?

I notice Apache is running multiple processes on my LAMP server (ubuntu 10.10). I'm just running a Wordpress site with MySQL as a database. It seems like www-data is running apache2 more than it ...
10
votes
2answers
810 views

Why is my RAID1 read access slower than write access?

I have done some simple performance tests and it seems that reading from my RAID1 is slower than writing: root@dss0:~# for i in 1 2 3; do dd if=/dev/zero of=/dev/sda bs=1048576 count=131072; done ...
10
votes
4answers
566 views

How do I most efficiently store and serve 1,000,000+ small gziped files on a Linux web server?

I have large static content that I have to deliver via a Linux-based webserver. It is a set of over one million small, gzip files. 90% of the files are less than 1K and the remaining files are at most ...
10
votes
2answers
1k views

How does Linux handle concurrent disk IO?

When a Linux server is serving many concurrent requests to read many different files, does it: Seek to File_1, read the entire file, then seek to File_2, read the entire file, then seek to File_3, ...
10
votes
2answers
318 views

Do unused application pools in IIS affect performance?

Due to a major update in our architecture, we now have a few unused application pools under IIS (there are no web sites mapped to them). I understand how it can a good idea to remove them just to ...
10
votes
1answer
3k views

Is calculating IOPS for ZFS RAIDZ different then calculating IOPS for RAID5 & RAID6?

When calculating IOPS for traditional RAID arrays, one could use the following formula (Borrowed from Getting The Hang Of IOPS v1.3 on Symantec Connect): Ieffective = (n * Isingle) / (READ% + (F * ...
10
votes
3answers
10k views

Incredibly slow KVM disk performance (qcow2 disk files + virtio)

I'm having some serious disk performance problems while setting up a KVM guest. Using a simple dd test, the partition on the host that the qcow2 images reside on (a mirrored RAID array) writes at ...
10
votes
3answers
324 views

Application “not supported” in a VM?

We bought some software from a small'ish company, it's a Windows 32-bit video content workflow manager, there's been some customisation by them. We've been working fine for over a year running this ...
10
votes
3answers
2k views

Extremely Slow IO with Simple PostgreSQL 8.4.4 Queries on Centos 5.5

The strange and extremely slow IO pattern I'm seeing is this (output of iostat -dxk 1 /dev/xvdb1): Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm ...
10
votes
3answers
576 views

Slow filesystem access

I'm trying to diagnose a slow filesystem issue on a server I look after. It's been ongoing for quite some time, and I've run out of ideas as to what I can try. Here's the thick of it. The server ...
10
votes
2answers
6k views

High disk I/O - jbd2/sda2-8 process

I have run a file server on a CentOS 5.8 final server. My only concern at the moment is what appears to be intermittent but continuous high disk I/O activity causing a general slowdown because of ...
9
votes
5answers
4k views

What purpose does an empty gif (1x1 pix) file serve?

I've seen a few random pages mention using empty gif images to somehow increase performance. I've also found the nginx has a module for just this purpose. What I can't figure out, is exactly how ...
9
votes
7answers
870 views

C:\ is for OS, D:\ is for Data?

"Back in the day" we always segregated our OS drives (in Windows) from our Data drives. In the Linux world, although I am much less familiar with it, I am aware that the wisdom dictates even more ...
9
votes
3answers
775 views

is it dangerous for the processor core to be *always* loaded at 100%?

In my HFT software I plan to use one core for stock index calculation. That would be simply while(true) loop without any delays which will calculate (sum and multiply) components as often as possible ...
9
votes
3answers
1k views

Configuring a router to drop packets, introduce latency, corrupt data

I was wondering if anyone had any experience setting up an environment designed purposefully for poor performance when sending/receiving requests over a network. I'm developing an application and ...
9
votes
9answers
2k views

On a modern system, will using disk compression give me better overall performance?

It seems that CPU increases have outpaced disk speed for a while. Assuming a desktop or laptop with modern dual core Intel/AMD CPU and a single average SATA disk, would doing compression on most all ...
9
votes
5answers
678 views

How do I find the cause for a huge difference in performance between two identical Ubuntu servers?

I am running two Dell R410 servers in the same rack of a data center (behind a load balancer). Both have the same hardware configuration, run Ubuntu 10.4, have the same packages installed and run the ...
9
votes
3answers
2k views

Methodologies for performance-testing a WAN link

We have a pair of new diversely-routed 1Gbps Ethernet links between locations about 200 miles apart. The 'client' is a new reasonably-powerful machine (HP DL380 G6, dual E56xx Xeons, 48GB DDR3, R1 ...
9
votes
2answers
949 views

Expected performance of e-SATA port multiplication?

For a certain read/write workload, I get 30 MiB/s from a 4-disk array using esata port multiplication. When I move the exact same array to four individual sata connections, I get 90 MiB/s for the same ...
9
votes
6answers
957 views

Accurately trending random I/O performance for capacity planning

Where I work we have a numerous "big iron" servers which are used used for hosting many virtual machines using a Xen Hypervisor. These are typically configured with 32GB RAM, Dual Quad core processes ...
9
votes
1answer
5k views

See what files are being written to (like iotop but for files, not processes)

I have a Linux server, and it's doing a lot of disk io. There is one process that is doing most of the disk writes. I found this out with iotop, which shows the processes that are doing disk I/O. Is ...