Thanks a lot! with the same underlying stripe/block size as of the image itself. If you wanted to write a 16 bytes to an image you can just pass it a 16 byte long slice (to use the Go term). Do you mean that if I pass the 10MiB bytes array to WriteAt func with default image configs it will strip it into 2 4MiB requests? for example, if I mount an Image to Linux I can specify the block size and each IO will be 4K for example and if I'm not wrong each op in Ceph will be 4K too. Now how can I simulate that behavior here too? I'm also facing an issue with go-ceph that with a 5-second interval I'm discarding and writing data to an image. After a while, for example, 30 sec the write will be stuck and it doesn't throw any error! How can I check what is wrong with it? cluster health is OK. On Thu, Dec 24, 2020 at 7:05 PM John Mulligan <phlogistonjohn(a)asynchrono.us> wrote: > On Thursday, December 24, 2020 8:25:15 AM EST Seena Fallah wrote: > > Hi, > > > > I want to write and read from an rbd image with librbd (librbdpy or > > go-ceph). I got some questions: > > > > I'll try to touch on some of the below for go-ceph specifically. However, > the > principles should generally apply to librdb (C) or python as all three > libraries are ultimately backed by the same stuff. Our naming should > largely > match what you'd find in librbd but occasionally we need to change things > a > little bit to match Go naming conventions and common interfaces [0]. > > > > 1. How can I do a random write/read with it? > > I would use the WriteAt [1] and ReadAt [2] calls on the Image type. > > > 2. How can I delete the written data with it? > > I'm not entirely clear on this question. You can delete an entire image. > Or > you could also zero out a range of data within the image either using > something like Discard [3] or WriteSame [4]. > > > 3. If I want to write with a for example 4K block size should I break my > > bytes array to 4K arrays by my self or librbd will do it on its own? > > with > the same underlying stripe/block size as of the image itself. If you > wanted to > write a 16 bytes to an image you can just pass it a 16 byte long slice (to > use > the Go term). > > You may find certain buffer sizes perform better than others, but the > library > doesn't require it, IIUC. > > > > 4. Does rbd_cache included in it? If yes how can I disable it? > > > > Unfortunately, I'm afraid I can't help with this one without more info as > I'm > not sure what it refers to. Perhaps someone with deeper experience > specifically > in rbd may know. > > I can say that go-ceph can load any ceph conf file, passing it to the > underlying ceph libraries, so if its something you can disable for the rbd > command line tool you ought to be able to do so for go-ceph [5]. > > > Thanks. > > [0] - We try to document what ceph API functions are being wrapped but > we're > not perfect and not all older code has had these "Implements" sections > added > to the inline docs. > [1] - https://pkg.go.dev/github.com/ceph/go-ceph@v0.7.0/rbd#Image.WriteAt > [2] - https://pkg.go.dev/github.com/ceph/go-ceph@v0.7.0/rbd#Image.ReadAt > [3] - https://pkg.go.dev/github.com/ceph/go-ceph@v0.7.0/rbd#Image.Discard > [4] - > https://pkg.go.dev/github.com/ceph/go-ceph@v0.7.0/rbd#Image.WriteSame > [5] - For rbd use the set up functions in the rados module to get an > IOContext. https://pkg.go.dev/github.com/ceph/go-ceph@v0.7.0/ > rados#Conn.ReadDefaultConfigFile - Please file issues with go-ceph if you > try it > and something does not work. > > >