On 01/06/2015 04:45 PM, Robert LeBlanc wrote:
Seems like a message bus would be nice. Each opener of an RBD could subscribe for messages on the bus for that RBD. Anytime the map is modified a message could be put on the bus to update the others. That opens up a whole other can of worms though.
Rados' watch/notify functions are used as a limited form of this. That's how rbd can notice that e.g. snapshots are created or disks are resized online. With the object map code the idea is to funnel all management operations like that through a single client that's locked the image for write access (all handled automatically by librbd). Using watch/notify to coordinate multi-client access would get complex and inefficient pretty fast, and in general is best left to cephfs rather than rbd. Josh
On Jan 6, 2015 5:35 PM, "Josh Durgin" <josh.durgin@xxxxxxxxxxx <mailto:josh.durgin@xxxxxxxxxxx>> wrote: On 01/06/2015 04:19 PM, Robert LeBlanc wrote: The bitmap certainly sounds like it would help shortcut a lot of code that Xiaoxi mentions. Is the idea that the client caches the bitmap for the RBD so it know which OSDs to contact (thus saving a round trip to the OSD), or only for the OSD to know which objects exist on it's disk? It's purely at the rbd level, so librbd caches it and maintains its consistency. The idea is that since it's kept consistent, librbd can do things like delete exactly the objects that exist without any extra communication with the osds. Many things that were O(size of image) become O(written objects in image). The only restriction is that keeping the object map consistent requires a single writer, so this does not work for the rare case of e.g. ocfs2 on top of rbd, where there are multiple clients writing to the same rbd image at once. Josh On Tue, Jan 6, 2015 at 4:19 PM, Josh Durgin <josh.durgin@xxxxxxxxxxx <mailto:josh.durgin@xxxxxxxxxxx>> wrote: On 01/06/2015 10:24 AM, Robert LeBlanc wrote: Can't this be done in parallel? If the OSD doesn't have an object then it is a noop and should be pretty quick. The number of outstanding operations can be limited to 100 or a 1000 which would provide a balance between speed and performance impact if there is data to be trimmed. I'm not a big fan of a "--skip-trimming" option as there is the potential to leave some orphan objects that may not be cleaned up correctly. Yeah, a --skip-trimming option seems a bit dangerous. This trimming actually is parallelized (10 ops at once by default, changeable via --rbd-concurrent-management-__ops) since dumpling. What will really help without being dangerous is keeping a map of object existence [1]. This will avoid any unnecessary trimming automatically, and it should be possible to add to existing images. It should be in hammer. Josh [1] https://github.com/ceph/ceph/__pull/2700 <https://github.com/ceph/ceph/pull/2700> On Tue, Jan 6, 2015 at 8:09 AM, Jake Young <jak3kaj@xxxxxxxxx <mailto:jak3kaj@xxxxxxxxx>> wrote: On Monday, January 5, 2015, Chen, Xiaoxi <xiaoxi.chen@xxxxxxxxx <mailto:xiaoxi.chen@xxxxxxxxx>> wrote: When you shrinking the RBD, most of the time was spent on librbd/internal.cc::trim___image(), in this function, client will iterator all unnecessary objects(no matter whether it exists) and delete them. So in this case, when Edwin shrinking his RBD from 650PB to 650GB, there are[ (650PB * 1024GB/PB -650GB) * 1024MB/GB ] / 4MB/Object = 170,227,200 Objects need to be deleted.That will definitely take a long time since rbd client need to send a delete request to OSD, OSD need to find out the object context and delete(or doesn’t exist at all). The time needed to trim an image is ratio to the size needed to trim. make another image of the correct size and copy your VM's file system to the new image, then delete the old one will NOT help in general, just because delete the old volume will take exactly the same time as shrinking , they both need to call trim_image(). The solution in my mind may be we can provide a “—skip-triming” flag to skip the trimming. When the administrator absolutely sure there is no written have taken place in the shrinking area(that means there is no object created in these area), they can use this flag to skip the time consuming trimming. How do you think? That sounds like a good solution. Like doing "undo grow image" From: Jake Young [mailto:jak3kaj@xxxxxxxxx <mailto:jak3kaj@xxxxxxxxx>] Sent: Monday, January 5, 2015 9:45 PM To: Chen, Xiaoxi Cc: Edwin Peer; ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> Subject: Re: rbd resize (shrink) taking forever and a day On Sunday, January 4, 2015, Chen, Xiaoxi <xiaoxi.chen@xxxxxxxxx <mailto:xiaoxi.chen@xxxxxxxxx>> wrote: You could use rbd info <volume_name> to see the block_name_prefix, the object name consist like <block_name_prefix>.<sequence___number>, so for example, rb.0.ff53.3d1b58ba.__00000000e6ad should be the <e6ad>th object of the volume with block_name_prefix rb.0.ff53.3d1b58ba. $ rbd info huge rbd image 'huge': size 1024 TB in 268435456 objects order 22 (4096 kB objects) block_name_prefix: rb.0.8a14.2ae8944a format: 1 -----Original Message----- From: ceph-users [mailto:ceph-users-bounces@__lists.ceph.com <mailto:ceph-users-bounces@xxxxxxxxxxxxxx>] On Behalf Of Edwin Peer Sent: Monday, January 5, 2015 3:55 AM To: ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> Subject: Re: rbd resize (shrink) taking forever and a day Also, which rbd objects are of interest? <snip> ganymede ~ # rados -p client-disk-img0 ls | wc -l 1672636 </snip> And, all of them have cryptic names like: rb.0.ff53.3d1b58ba.__00000000e6ad rb.0.6d386.1d545c4d.__000000011461 rb.0.50703.3804823e.__000000001c28 rb.0.1073e.3d1b58ba.__00000000b715 rb.0.1d76.2ae8944a.__00000000022d which seem to bear no resemblance to the actual image names that the rbd command line tools understands? Regards, Edwin Peer On 01/04/2015 08:48 PM, Jake Young wrote: On Sunday, January 4, 2015, Dyweni - Ceph-Users <6EXbab4FYk8H@xxxxxxxxxx <mailto:6EXbab4FYk8H@xxxxxxxxxx> <mailto:6EXbab4FYk8H@dyweni.__com <mailto:6EXbab4FYk8H@xxxxxxxxxx>>> wrote: Hi, If its the only think in your pool, you could try deleting the pool instead. I found that to be faster in my testing; I had created 500TB when I meant to create 500GB. Note for the Devs: I would be nice if rbd create/resize would accept sizes with units (i.e. MB GB TB PB, etc). On 2015-01-04 08:45, Edwin Peer wrote: Hi there, I did something stupid while growing an rbd image. I accidentally mistook the units of the resize command for bytes instead of megabytes and grew an rbd image to 650PB instead of 650GB. This all happened instantaneously enough, but trying to rectify the mistake is not going nearly as well. <snip> ganymede ~ # rbd resize --size 665600 --allow-shrink client-disk-img0/vol-x318644f-__0 Resizing image: 1% complete... </snip> It took a couple days before it started showing 1% complete and has been stuck on 1% for a couple more. At this rate, I should be able to shrink the image back to the intended size in about 2016. Any ideas? Regards, Edwin Peer _________________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/__listinfo.cgi/ceph-users-ceph.__com <http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com> _________________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/__listinfo.cgi/ceph-users-ceph.__com <http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com> You can just delete the rbd header. See Sebastien's excellent blog: http://www.sebastien-han.fr/__blog/2013/12/12/rbd-image-__bigger-than-your <http://www.sebastien-han.fr/blog/2013/12/12/rbd-image-bigger-than-your> -ceph-cluster/ Jake _________________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/__listinfo.cgi/ceph-users-ceph.__com <http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com> _________________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/__listinfo.cgi/ceph-users-ceph.__com <http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com> _________________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/__listinfo.cgi/ceph-users-ceph.__com <http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com> Sorry, I misunderstood. The simplest approach to me is to make another image of the correct size and copy your VM's file system to the new image, then delete the old one. The safest thing to do would be to mount the new file system from the VM and do all the formatting / copying from there (the same way you'd move a physical server's root disk to a new physical disk) I would not attempt to hack the rbd header. You open yourself up to some unforeseen problems. Unless one of the ceph developers can comment there is a safe way to shrink an image, assuming we know that the file system has not grown since growing the disk. Jake
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