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diff --git a/done/GlusterFS 3.5/Zerofill.md b/done/GlusterFS 3.5/Zerofill.md new file mode 100644 index 0000000..43b279d --- /dev/null +++ b/done/GlusterFS 3.5/Zerofill.md @@ -0,0 +1,192 @@ +Feature +------- + +zerofill API for GlusterFS + +Summary +------- + +zerofill() API would allow creation of pre-allocated and zeroed-out +files on GlusterFS volumes by offloading the zeroing part to server +and/or storage (storage offloads use SCSI WRITESAME). + +Owners +------ + +Bharata B Rao +M. Mohankumar + +Current status +-------------- + +Patch on gerrit: <http://review.gluster.org/5327> + +Detailed Description +-------------------- + +Add support for a new ZEROFILL fop. Zerofill writes zeroes to a file in +the specified range. This fop will be useful when a whole file needs to +be initialized with zero (could be useful for zero filled VM disk image +provisioning or during scrubbing of VM disk images). + +Client/application can issue this FOP for zeroing out. Gluster server +will zero out required range of bytes ie server offloaded zeroing. In +the absence of this fop, client/application has to repetitively issue +write (zero) fop to the server, which is very inefficient method because +of the overheads involved in RPC calls and acknowledgements. + +WRITESAME is a SCSI T10 command that takes a block of data as input and +writes the same data to other blocks and this write is handled +completely within the storage and hence is known as offload . Linux ,now +has support for SCSI WRITESAME command which is exposed to the user in +the form of BLKZEROOUT ioctl. BD Xlator can exploit BLKZEROOUT ioctl to +implement this fop. Thus zeroing out operations can be completely +offloaded to the storage device , making it highly efficient. + +The fop takes two arguments offset and size. It zeroes out 'size' number +of bytes in an opened file starting from 'offset' position. + +Benefit to GlusterFS +-------------------- + +Benefits GlusterFS in virtualization by providing the ability to quickly +create pre-allocated and zeroed-out VM disk image by using +server/storage off-loads. + +### Scope + +Nature of proposed change +------------------------- + +An FOP supported in libgfapi and FUSE. + +Implications on manageability +----------------------------- + +None. + +Implications on presentation layer +---------------------------------- + +N/A + +Implications on persistence layer +--------------------------------- + +N/A + +Implications on 'GlusterFS' backend +----------------------------------- + +N/A + +Modification to GlusterFS metadata +---------------------------------- + +N/A + +Implications on 'glusterd' +-------------------------- + +N/A + +How To Test +----------- + +Test server offload by measuring the time taken for creating a fully +allocated and zeroed file on Posix backend. + +Test storage offload by measuring the time taken for creating a fully +allocated and zeroed file on BD backend. + +User Experience +--------------- + +Fast provisioning of VM images when GlusterFS is used as a file system +backend for KVM virtualization. + +Dependencies +------------ + +zerofill() support in BD backend depends on the new BD translator - +<http://review.gluster.org/#/c/4809/> + +Documentation +------------- + +This feature add support for a new ZEROFILL fop. Zerofill writes zeroes +to a file in the specified range. This fop will be useful when a whole +file needs to be initialized with zero (could be useful for zero filled +VM disk image provisioning or during scrubbing of VM disk images). + +Client/application can issue this FOP for zeroing out. Gluster server +will zero out required range of bytes ie server offloaded zeroing. In +the absence of this fop, client/application has to repetitively issue +write (zero) fop to the server, which is very inefficient method because +of the overheads involved in RPC calls and acknowledgements. + +WRITESAME is a SCSI T10 command that takes a block of data as input and +writes the same data to other blocks and this write is handled +completely within the storage and hence is known as offload . Linux ,now +has support for SCSI WRITESAME command which is exposed to the user in +the form of BLKZEROOUT ioctl. BD Xlator can exploit BLKZEROOUT ioctl to +implement this fop. Thus zeroing out operations can be completely +offloaded to the storage device , making it highly efficient. + +The fop takes two arguments offset and size. It zeroes out 'size' number +of bytes in an opened file starting from 'offset' position. + +This feature adds zerofill support to the following areas: + +- libglusterfs +- io-stats +- performance/md-cache,open-behind +- quota +- cluster/afr,dht,stripe +- rpc/xdr +- protocol/client,server +- io-threads +- marker +- storage/posix +- libgfapi + +Client applications can exploit this fop by using glfs\_zerofill +introduced in libgfapi.FUSE support to this fop has not been added as +there is no system call for this fop. + +Here is a performance comparison of server offloaded zeofill vs zeroing +out using repeated writes. + + [root@llmvm02 remote]# time ./offloaded aakash-test log 20 + + real 3m34.155s + user 0m0.018s + sys 0m0.040s + + + [root@llmvm02 remote]# time ./manually aakash-test log 20 + + real 4m23.043s + user 0m2.197s + sys 0m14.457s + [root@llmvm02 remote]# time ./offloaded aakash-test log 25; + + real 4m28.363s + user 0m0.021s + sys 0m0.025s + [root@llmvm02 remote]# time ./manually aakash-test log 25 + + real 5m34.278s + user 0m2.957s + sys 0m18.808s + +The argument log is a file which we want to set for logging purpose and +the third argument is size in GB . + +As we can see there is a performance improvement of around 20% with this +fop. + +Status +------ + +Patch : <http://review.gluster.org/5327> Status : Merged
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