Unfortunately that kind of tuning doesn't have any simple answers, and any one who says there is should not be listened to. It really depends on your workload and a lot of other factors such as your hardware. for example a 20 plater RAID 1+0 on spinning disks with a wide stripe needs very little cache for streaming large (MultiGB) files due to the large IOPS they can do, but would need a large cache for lots of files smaller than the stripe due to the fact that each file access is a minimum of 1 IOP which means a full read of the stripe. The reverse may be true if the files are only 4k or less on average, in which case a standalone SATA SSD would be way faster and need very little cache,but on large (MultiGB) files it would need a huge amount of cache due to the 4k per IOP size limitation in SSD's. Furthermore those scenarios assume your filesystem is correctly aligned, unfortunately they usually aren't. The reasons for this are complicated but in short the drivers (and in many cases the chipsets) for many RAID and SATA controllers do not provide the information the OS (/sys, LVM, and the filesystem) requires to align the filesystem automatically when its created. Now most DBA's will tell you they need an insane number of IOPs, what they are really telling you is how many operations the database is doing, not how many IOP's its doing. In reality databases do surprisingly few IOPs and tend more to do large (MultiGB) sequential reads into the ram used by the database processes, then do all their operations there. Also an other key factor is the IO scheduler (elevator="....." in the kernel boot options) you are using in the kernel. CFQ which is the default is great for desktops and servers running the 10 or more different services on inexpensive hardware. on most dedicated servers deadline or possibly if you have a good raid controller noop is much better. using the proper IO scheduler can have a dramatic impact on how much ram you use for cache, especially for writes. As I said there is no easy answer to this but if you can give us an idea of the typical workload then we may be able to give some advice. On Fri, May 27, 2016 at 8:27 AM, kostas makedos <kostas.makedos@xxxxxxxxx> wrote: > Hello, > Can someone give me an estimate ratio between RAM consumption in > a node in respect to the GB stored in its bricks? > Is there a rule of thumb or a guideline document? > > > Thank you, > > Best Regards > Kostas Makedos > > kostas.makedos@xxxxxxxxx > > > > _______________________________________________ > Gluster-users mailing list > Gluster-users@xxxxxxxxxxx > http://www.gluster.org/mailman/listinfo/gluster-users _______________________________________________ Gluster-users mailing list Gluster-users@xxxxxxxxxxx http://www.gluster.org/mailman/listinfo/gluster-users
