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

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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 GFS2 cluster?

Best Answer

If they are opened read-only on each node, they are cached locally. It depends on how the files are lock

Related Solutions

Use ext3 as a shared fs if I add a lock manager

NO. The main reason is that the filesystem cache is not cluster aware and is not coherent, so you end up mangling your data.

Try mounting the ext3 FS in two boxes, create a file in one box and see if it appears in the other...

Linux – How to see if the disk cache is disabled on Linux

Your VPS is running under Virtuozzo/OpenVZ. In this setup, it's not a true fully-segregated VM as would be the case with say Xen or VMware. With OpenVZ and Virtuozzo, there is one single instance of the kernel running (instead of one per VM), and this kernel is responsible for maintaining separation between all of the processes running under the different guest VMs. This includes managing the disk caching layer. Because this function is operating outside of your VM, you don't have any visibility into what your cache looks like.

I'm not sure if this is an issue specifically with your host's implementation of OpenVZ or if it's just a side-affect of how OpenVZ does virtualization.

As an aside, I checked on the one OpenVZ VM I have access to, and wasn't able to see cache info there either. If you need access to this information, I'd recommend moving to a VPS provider that uses Xen or some other real hypervisor.

Best Answer

Related Solutions

Use ext3 as a shared fs if I add a lock manager

Linux – How to see if the disk cache is disabled on Linux

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