On April 8, 2020 10:15:27 PM GMT+03:00, Erik Jacobson <erik.jacobson@xxxxxxx> wrote: >I wanted to share some positive news with the group here. > >Summary: Using sharding and squashfs image files instead of expanded >directory trees for RO NFS OS images have led to impressive boot times >of >2k diskless node clusters using 12 servers for gluster+tftp+etc+etc. > >Details: > >As you may have seen in some of my other posts, we have been using >gluster to boot giant clusters, some of which are in the top500 list of >HPC resources. The compute nodes are diskless. > >Up until now, we have done this by pushing an operating system from our >head node to the storage cluster, which is made up of one or more >3-server/(3-brick) subvolumes in a distributed/replicate configuration. >The servers are also PXE-boot and tftboot servers and also serve the >"miniroot" (basically a fat initrd with a cluster manager toolchain). >We also locate other management functions there unrelated to boot and >root. > >This copy of the operating system is a simple a directory tree >representing the whole operating system image. You could 'chroot' in to >it, for example. > >So this operating system is a read-only NFS mount point used as a base >by all compute nodes to use as their root filesystem. > >This has been working well, getting us boot times (not including BIOS >startup) of between 10 and 15 minutes for a 2,000 node cluster. >Typically a >cluster like this would have 12 gluster/nfs servers in 3 subvolumes. On >simple >RHEL8 images without much customization, I tend to get 10 minutes. > >We have observed some slow-downs with certain job launch work loads for >customers who have very metadata intensive job launch. The metadata >load >of such an operation is very intensive, with giant loads being observed >on the gluster servers. > >We recently started supporting RW NFS as opposed to TMPFS for this >solution for the writable components of root. Our customers tend to >prefer >to keep every byte of memory for jobs. We came up with a solution of >hosting >the RW NFS sparse files with XFS filesystems on top from a writable >area in >gluster for NFS. This makes the RW NFS solution very fast because it >reduces >RW NFS metadata per-node. Boot times didn't go up significantly (but >our >first attempt with just using a directory tree was a slow disaster, >hitting >the worse-case lots of small file write + lots of metadata work load). >So we >solved that problem with XFS FS images on RW NFS. > >Building on that idea, we have in our development branch, a version of >the >solution that changes the RO NFS image to a squashfs file on a sharding >volume. That is, instead of each operating system being many thousands >of files and being (slowly) synced to the gluser servers, the head node >makes a squashfs file out of the image and pushes that. Then all the >compute nodes mount the squashfs image from the NFS mount. > (mount RO NFS mount, loop-mount squashfs image). > >On a 2,000 node cluster I had access to for a time, our prototype got >us >boot times of 5 minutes -- including RO NFS with squashfs and the RW >NFS >for writable areas like /etc, /var, etc (on an XFS image file). > * We also tried RW NFS with OVERLAY and no problem there > >I expect, for people who prefer the squashfs non-expanded format, we >can >reduce the leader per compute density. > >Now, not all customers will want squashfs. Some want to be able to edit >a file and see it instantly on all nodes. However, customers looking >for >fast boot times or who are suffering slowness on metadata intensive >job launch work loads, will have a new fast option. > >Therefore, it's very important we still solve the bug we're working on >in another thread. But I wanted to share something positive. > >So now I've said something positive instead of only asking for help :) >:) > >Erik >________ > > > >Community Meeting Calendar: > >Schedule - >Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC >Bridge: https://bluejeans.com/441850968 > >Gluster-users mailing list >Gluster-users@xxxxxxxxxxx >https://lists.gluster.org/mailman/listinfo/gluster-users Good Job Erik! Best Regards, Strahil Nikolov ________ Community Meeting Calendar: Schedule - Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC Bridge: https://bluejeans.com/441850968 Gluster-users mailing list Gluster-users@xxxxxxxxxxx https://lists.gluster.org/mailman/listinfo/gluster-users
