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1answer
36 views

Can high disk cache usage lead to external fragmentation and ultimately to page allocation failures?

We're getting page allocation failures on a Linux server (3.2 kernel). We've been told the problem is directly related to the high use of the memory for cache; this would lead to external ...
2
votes
1answer
134 views

Linux read disk cache and NFS

I am interested in the impact of the read disk cache on accessing a file through NFS. Lets say I have a file on NFS. I access it (do "cat myfile") from a linux host "A". If there's enough RAM a file ...
0
votes
0answers
170 views

On a system with 64GB mem the Linux Buffer run full while copying with dd to dev null and io stops till manual drop_caches

I am running a server with linux software raid 10. It is a dual CPU system with 64GB Ram. 2x16GB dimms related to each of the CPUs. I want to use dd to backup kvm virtual machines and run into a ...
1
vote
1answer
197 views

Why is mongod not using all available RAM?

We have an mongod instance runnning on a VM, and it doesn't seem to be using all available memory. It's page-faulting significantly more than usual, and the system's performance has been significantly ...
0
votes
0answers
175 views

Invalid command 'CacheIgnoreURLSessionIdentifiers', perhaps misspelled or defined by a module not included in the server configuration

I plan to add the caching module in Apache2. If I add the following lines in the Configuration it works fine. <IfModule mod_disk_cache.c> SetEnvIf Request_URI !\.(|pdf|jpg|jpeg|png|gif|)$ ...
0
votes
1answer
136 views

Linux not freeing the file buffer when we execute rm or > (redirection) operator

I have one router which has embedded-linux with kernel version 2.4.22 running on it. I know its very old version but i have to deal with it. Please take a look at the free command output when i run it ...
0
votes
1answer
120 views

nginx proxy_cache or Memcached

I currently use nginx's proxy_cache for file-based caching in front of three Django applications (Apache/mod_wsgi). For some locations/URLs, I disabled proxy_cache and used Memcached (per view) within ...
0
votes
1answer
142 views

ram disk mirroring part of physical disk

What I would like to do/have is: Some kind of application/driver that creates a RAM drive/partition that is actually assigned a drive letter (eg. D:). This drive letter should be based on/mirroring a ...
3
votes
2answers
526 views

Write caching in linux

I have read a lot on serverfault and searched on google about write caching, but still cant find the answer. I have an HP ProLiant DL380 G5 with HW raid with 512 MB Battery backed cache. I use debian ...
1
vote
1answer
188 views

Apache mod cache mem/disk saves the cache for 10 seconds and than re-cache

I have this set up in my 000-default: <VirtualHost 192.168.1.10:80> ServerName live.website.com DocumentRoot /var/www/live.website.com SetOutputFilter INFLATE;proxy-html;DEFLATE ...
12
votes
2answers
820 views

Safety of write cache on SATA drives with barriers

I've been reading lately about write caching, NCQ, firmware bugs, barriers, etc regarding SATA drives, and I'm not sure what's the best setting that would make my data safe in case of a power failure. ...
3
votes
1answer
49 views

varnish delete least requested files

I see that varnish can be configured to set -smalloc or -sfile with a certain size. I want to set a file cache of 1G such that least requested files are deleted first when cache is full. Is this ...
1
vote
0answers
148 views

Disk cache (write back) disables automatically

some days ago I discovered (using Munin) that my server had high iowait times. The reason was that write cache was disabled. I enabled it using hdparm -W1 /dev/sda but after some time (ramdonly) it ...
2
votes
1answer
412 views

Solaris 10: Drop disk cache? (to benchmark app)

Is there a command to drop the ZFS and UFS disk caches? (Preferably just one folder hierarchy.) I'm trying to tuning the performance settings of an application that read/writes data from a large ...
1
vote
0answers
344 views

Mod disk_cache permanent caching images and disabling reacurring header updates

I am trying to get mod disk_cache to permantly cache images retrieved from an image server on the webserver using ProxyPass. While the image is being retrieved correctly from the server and is served ...
2
votes
1answer
93 views

CentOS VM only using a third of available memory

I have a VM slice running CentOS, on Parallels. Here is the output of free -m [root@server ~]# free -m total used free shared buffers cached Mem: 960 ...
3
votes
2answers
3k views

Should I disable write caching on my Windows 2008 VM?

I have a Windows Server 2008 x64 Standard virtual machine that runs on a machine with a hardware RAID controller, a Perc 6/i, which has a battery on-board. Doing everything I can for additional ...
2
votes
4answers
667 views

Would a PHP application benefit from being served from a RAM drive?

I am in charge of hosting a PHP application that is large and slow, but easy to scale. The application is entirely static, with writable disk storage needed. We've profiled the application, and the ...
2
votes
1answer
2k views

High disk I/O activity in CentOS server

I have about 16 websites in a CentOS dedicated, and I am having some problems on high traffic hours, it seems to be a high disk I/O activity causing a general slowdown. I've installed atop and this ...
0
votes
1answer
523 views

Which Linux filesystem is best for a huge Apache mod_disk_cache partition?

Talking about a huge (50GB, 500.000 entries) Apache disk_cache partition: Which Linux filesystem performs best for this task? In my example, the partition has a lot (500.000) of very small files ...
3
votes
1answer
3k views

Linux not freeing large disk cache when memory demand goes up

Running Ubuntu on a 2.6.31-302 x86-64 kernel. The overall problem is that I have memory in the 'cached' category that keeps on going up and will not be freed or used even when our application needs ...
0
votes
1answer
450 views

Linux server with JBoss , the system cache increased each day

We run an Apache Mod_proxy cluster with 3 JBoss in three dedicated server. Because we need share many files (small object files which our apps need to read/write ) between these JBoss servers ,we ...
5
votes
3answers
3k views

Why does mdadm write unusably slow when mounted synchronously?

I have a 6 disk raid6 mdadm array I'd like to benchmark writes to: root@ubuntu:~# cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] md0 : active raid6 sda[0] sdf[5] sde[4] sdd[3] sdc[2] ...
1
vote
1answer
2k views

How do I see if my disk cache is disabled on Linux?

I have an ubuntu linux virtual machine here and I think there is no disk cache. For example this is the output from free -m: total used free shared buffers ...
0
votes
1answer
3k views

What is read cache in “[sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA”?

I'm trying to figure out what the read cache part of the following message refers to: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA Is it "IDE drive's ...
0
votes
1answer
561 views

Raid Caching configuration suggestions

I'm wondering if there's the optimal Cache setting for the following Raid controllers and raid setups. (OS: windows 2008 R2, App: II7, DB: SQL Server 2008 R2 Enterprise) PERC 6/i: (The default ...
2
votes
1answer
845 views

How Does The Linux Disk Cache Work With iSCSI and GFS2?

I'm planning to share a GFS2 filesystem via iSCSI to my web servers. Are the files read by my web servers cached locally using the linux disk cache stored in memory or are they only cached on the ...
3
votes
1answer
2k views

How much does HDD cache matter with Linux softraid?

I'm in a process of renewing/expanding my disk sets, but not quite sure what kind of disks to get, cache-wise. What difference does disk cache amount of 16/32/64MB do, in capacities of, say, ...
2
votes
4answers
6k views

Store Varnish cache in hard disk

The situation is: Im building PHP application, and need http caching. Varnish is great, and lots of people tell me that Varnish store the cached data in RAM. But I want it cached in hard disk. Is ...
4
votes
5answers
6k views

Disable all disk caching for apache2 on linux

For benchmarking purposes I want to force Apache 2 to load each requested file from disk instead of loading it from a cache in memory. From what I have read doing a sync followed by echo 3 > ...
4
votes
9answers
7k views

Rapid SSD vs. RAM in servers

Per GB prices of rapid SSD (like Intel X25-E) come close to prices of high-end RAM. So what extra advantages does SSD give you? What are particular reasons, why you buy SSD, instead of just putting ...