Linux Read-Ahead Downsides

Posted by JPerkSter on Server Fault See other posts from Server Fault or by JPerkSter
Published on 2010-06-03T21:28:45Z Indexed on 2010/06/03 21:35 UTC
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Hi Everyone,

Hope all is well. I have a question regarding read-ahead caching.

Are there any downsides to raising the size of the read-ahead cache?

On our farm, we're currently running at 256, and upon raising that higher, we are seeing significant throughput gains.

 

[root@server~]# hdparm -tT /dev/sda /dev/sda: 
Timing cached reads: 7352 MB in 2.00 seconds = 3677.62 MB/sec 3
Timing buffered disk reads: 244 MB in 3.10 seconds = 78.68 MB/sec 

[root@server ~]# blockdev --setra 10240 /dev/sda 

[root@server ~]# hdparm -tT /dev/sda /dev/sda: 
Timing cached reads: 11452 MB in 2.00 seconds = 5728.52 MB/sec 
Timing buffered disk reads: 422 MB in 3.17 seconds = 133.04 MB/sec

We are running on 2.6. Thanks!

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