Questions tagged [disk-cache]

Disk-cache: reserved area in RAM to speed-up disk access

A disk cache is a cache memory that is used to speed up the process of storing and accessing data from the host hard disk. It enables faster processing of reading/writing, commands and other input and output process between the hard disk, the memory and computing components.

The memory can be part of the disk drive itself (sometimes called a hard disk cache or buffer) or it can be general-purpose RAM in the computer that is reserved for use by the disk drive (sometimes called a soft disk cache). Hard disk cachesare more effective, but they are also much more expensive, and therefore smaller. Nearly all modern disk drives include a small amount of internal cache.

54 questions
25
votes
2 answers

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 it. So here's what I get out of the 'free' command.…
trisweb
  • 481
  • 1
  • 5
  • 10
14
votes
2 answers

How to setup an NFS server that caches a network share?

User data is stored on two fairly large (>1 PB) OpenStack Swift storage clusters. Let them be Cluster A and Cluster B. In addition, there are several PoPs that need to interact with that data. Servers in these PoPs are effectively diskless, meaning…
mınxomaτ
  • 240
  • 2
  • 7
14
votes
2 answers

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. From what I understand, NCQ allows the drive to…
julianjm
  • 270
  • 2
  • 5
8
votes
2 answers

Are bcache and/or dm-cache considered stable for production in 2016?

I would like to use linux SSD caching (dm-cache or bcache) with Debian Jessie production servers. (kernel 3.16) My question: Are dm-cache and bcache modules reliables in linux 3.16 ? Do I need to upgrade my kernel to a more recent version ? I also…
sligor
  • 83
  • 1
  • 5
8
votes
3 answers

Use Varnish Cache only on-disk

The situation is: I' m building a PHP application and need http caching. Varnish is great and lots of people tell me that Varnish stores the cached data in RAM. I want it to cache on hard disk. Is there any way to store the Varnish cache-data on…
Great Kuma
7
votes
2 answers

Windows Server virtual disk cache settings

In Windows under Azure or Hyper-V, the Disk Policy write cache settings for a virtual disk will always appear to be enabled from the server configuration, regardless of the actual status of write cache settings on the underlying disk system.…
wst
  • 171
  • 1
  • 4
7
votes
4 answers

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 > /proc/sys/vm/drop_caches lets me drop linux's cache. A…
davitenio
  • 375
  • 2
  • 5
  • 10
6
votes
9 answers

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 more RAM in your server machine, to have it used…
vartec
  • 6,137
  • 2
  • 32
  • 49
6
votes
3 answers

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] sdb[1] 1953545984 blocks level 6, 64k chunk,…
chrishiestand
  • 974
  • 12
  • 23
5
votes
1 answer

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 would end up in the disk cache. Now I modify that…
Janek
  • 153
  • 1
  • 4
5
votes
4 answers

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 performance, I think I should disable this. Is this…
jwbensley
  • 4,122
  • 11
  • 57
  • 89
4
votes
1 answer

Linux - Disk / Filesystem as a LRU Cache (with transparent expiry)

I have a case where I'd want to use local disk as a LRU cache for (hot) files from a separate web service (something like S3). If the file doesn't exist on disk, the file is read over the internet, written to the local disk and then future requests…
fiskfisk
  • 151
  • 5
4
votes
1 answer

Disable file cache for mount point

I ran into a bug similar to this one: RHEL NFS client returns NULL bytes when reading a growing file So my solution was to check for \0 Bytes and reread the file. Problem here is, that the wrong file, which includes the \0 Bytes, is cached on the…
robin.koch
  • 141
  • 1
  • 4
4
votes
2 answers

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 linux. There are 3 write caches: 1. OS write…
Jozko
  • 43
  • 1
  • 3
4
votes
1 answer

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 number of files. Mostly read. In actual use, the app…
nonot1
  • 1,069
  • 1
  • 12
  • 16
1
2 3 4