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> in fact, in most cases, there is no filesystem at all Huh? With few exceptions, applications write to disk using a VFS provided by an operating system. Can y
by jonhohle 3y ago
> in fact, in most cases, there is no filesystem at all
Huh? With few exceptions, applications write to disk using a VFS provided by an operating system. Can you provide an example of cloud storage that uses raw disks (bypassing VFS)?
There also isn’t a POSIX file system, just POSIX compatible file systems. Those file systems may expose non-POSIX APIs to do other low level work (trim, clone, snapshot, etc.).
- cuno 3y agoHi, similar to nvm0n2 who already commented below, object storage systems often directly write to block storage rather than through a VFS. While minio, for example, can run on top of a VFS, even they say you shouldn't be - you should instead run it directly on block storage across multiple drives / nodes.
- IcePic 3y agoCEPH would be one of those, which is more like a database using raw devices, and no linux filesystem (nor VFS calls) in between. It used to run on top of xfs, but now storage nodes (OSDs) talks directly to a raw device (or an lvm on top of it). But you can most certainly not run "ls" on such a host and get a listing of what some user wrote over S3 into it.
- jonhohle 3y agoAre there any benchmarks that justify bypassing VFS? My Google-fu is failing and the one page I found comparing file systems in the CEPH docs doesn’t talk about raw access, all images are broken (stored on CEPH raw storage?), and the text doesn’t seem to include throughout numbers.
- tryauuum 3y agohttps://www.pdl.cmu.edu/PDL-FTP/Storage/ceph-exp-sosp19.pdf https://www.pdl.cmu.edu/PDL-FTP/Storage/ceph-exp-sosp19.pdf my google-fu found this it's hard to read and summarize. It seems that the main point is that filesystems don't expose many tools ceph needs
- IcePic 3y agoIf you store stuff on xfs or ext4, it will cause more writes due to the journal, and since ceph is a DB in some sense, it also keeps a journal/WAL so doubling that is a waste.
- LightFog 3y agoIt’s not uncommon for high performance object stores to bypass POSIX FS semantics and provide kernel patches etc - eg lustre do this.