Vickey, OSDs are on top of filesystem and those unused memory will be automatically part of paged cache by filesystem. But, the read performance improvement depends on the pattern application is reading data and the size of working set. Sequential pattern will benefit most (you may need to tweak read_ahead_kb to bigger values). For random workload also you will get benefit if the working set is not too big. For example, a LUN of say 1 TB and aggregated OSD page cache of say of 200GB will benefit more than a LUN of say 100TB with the similar amount of page cache (considering a true random pattern).
Thanks & Regards Somnath From: ceph-users [mailto:[email protected]] On Behalf Of Vickey Singh Sent: Monday, September 07, 2015 2:19 PM To: [email protected] Subject: [ceph-users] Extra RAM use as Read Cache Hello Experts , I want to increase my Ceph cluster's read performance. I have several OSD nodes having 196G RAM. On my OSD nodes Ceph just uses 15-20 GB of RAM. So, can i instruct Ceph to make use of the remaining 150GB+ RAM as read cache. So that it should cache data in RAM and server to clients very fast. I hope if this can be done, i can get a good read performance boost. By the way we have a LUSTRE cluster , that uses extra RAM as read cache and we can get upto 2.5GBps read performance. I am looking someone to do with Ceph. - Vickey - ________________________________ PLEASE NOTE: The information contained in this electronic mail message is intended only for the use of the designated recipient(s) named above. If the reader of this message is not the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify the sender by telephone or e-mail (as shown above) immediately and destroy any and all copies of this message in your possession (whether hard copies or electronically stored copies).
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