* [Qemu-devel] drive-backup @ 2016-02-22 20:21 Stefan Priebe 2016-02-22 22:08 ` John Snow 0 siblings, 1 reply; 6+ messages in thread From: Stefan Priebe @ 2016-02-22 20:21 UTC (permalink / raw) To: qemu-devel; +Cc: Timo Grodzinski Hello, is there any chance or hack to work with a bigger cluster size for the drive backup job? See: http://git.qemu.org/?p=qemu.git;a=blob;f=block/backup.c;h=16105d40b193be9bb40346027bdf58e62b956a96;hb=98d2c6f2cd80afaa2dc10091f5e35a97c181e4f5 This is very slow with ceph - may be due to the 64k block size. I would like to check whether this is faster with cephs native block size of 4mb. Greets, Stefan ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] drive-backup 2016-02-22 20:21 [Qemu-devel] drive-backup Stefan Priebe @ 2016-02-22 22:08 ` John Snow 2016-02-25 7:49 ` Stefan Priebe - Profihost AG 0 siblings, 1 reply; 6+ messages in thread From: John Snow @ 2016-02-22 22:08 UTC (permalink / raw) To: Stefan Priebe, qemu-devel; +Cc: Timo Grodzinski, Qemu-block On 02/22/2016 03:21 PM, Stefan Priebe wrote: > Hello, > > is there any chance or hack to work with a bigger cluster size for the > drive backup job? > > See: > http://git.qemu.org/?p=qemu.git;a=blob;f=block/backup.c;h=16105d40b193be9bb40346027bdf58e62b956a96;hb=98d2c6f2cd80afaa2dc10091f5e35a97c181e4f5 > > > This is very slow with ceph - may be due to the 64k block size. I would > like to check whether this is faster with cephs native block size of 4mb. > > Greets, > Stefan > It's hardcoded to 64K at the moment, but I am checking in a patch to round up the cluster size to be the bigger of (64k, $target_cluster_size) in order to make sure that incremental backups in particular never copy a fraction of a cluster. As a side-effect, the same round-up will happen for all modes (sync=top,none,full). If QEMU is aware of the target cluster size of 4MB, this would immediately jump the copy-size up to 4MB clusters for you. See: https://lists.nongnu.org/archive/html/qemu-devel/2016-02/msg02839.html Otherwise, after my trivial fix, you should find cluster_size to be a mutable concept and perhaps one that you could introduce a runtime parameter for if you could convince the necessary parties that it's needed in the API. You'd have to be careful in the case of incremental that all the various cluster sizes work well together: - Granularity of bitmap (Defaults to cluster size of source, or 64K if unknown. can be configured to be arbitrarily larger.) - Cluster size of source file (For qcow2, defaults to 64k) - Cluster size of target file - Cluster size of backup routine (Currently always 64K) I think that LCM(source_cluster_size, target_cluster_size, backup_cluster_size) = MAX(A, B, C) will always be a safe minimum. Bitmap granularity is more flexible, and it is more efficient when the bitmap granularity matches the backup cluster size, but it can cope with mismatches. If the bitmap is smaller or larger than the backup cluster size, it generally means that more data that is clean is going to be transferred across the pipe. (Hmm, I wonder if it's worth checking in code to adjust a bitmap granularity after it has been created so people can easily experiment with performance tweaking here.) Let me know if any of my ramble sounds interesting :) --John ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] drive-backup 2016-02-22 22:08 ` John Snow @ 2016-02-25 7:49 ` Stefan Priebe - Profihost AG 2016-02-25 7:59 ` Fam Zheng 2016-02-25 19:53 ` John Snow 0 siblings, 2 replies; 6+ messages in thread From: Stefan Priebe - Profihost AG @ 2016-02-25 7:49 UTC (permalink / raw) To: John Snow, qemu-devel; +Cc: Timo Grodzinski, Qemu-block Am 22.02.2016 um 23:08 schrieb John Snow: > > > On 02/22/2016 03:21 PM, Stefan Priebe wrote: >> Hello, >> >> is there any chance or hack to work with a bigger cluster size for the >> drive backup job? >> >> See: >> http://git.qemu.org/?p=qemu.git;a=blob;f=block/backup.c;h=16105d40b193be9bb40346027bdf58e62b956a96;hb=98d2c6f2cd80afaa2dc10091f5e35a97c181e4f5 >> >> >> This is very slow with ceph - may be due to the 64k block size. I would >> like to check whether this is faster with cephs native block size of 4mb. >> >> Greets, >> Stefan >> > > It's hardcoded to 64K at the moment, but I am checking in a patch to > round up the cluster size to be the bigger of (64k, > $target_cluster_size) in order to make sure that incremental backups in > particular never copy a fraction of a cluster. As a side-effect, the > same round-up will happen for all modes (sync=top,none,full). > > If QEMU is aware of the target cluster size of 4MB, this would > immediately jump the copy-size up to 4MB clusters for you. > > See: https://lists.nongnu.org/archive/html/qemu-devel/2016-02/msg02839.html Thanks for your patches and thanks for your great answer. But our problem is not the target but the source ;-) The target has a local cache and don't care about the cluster size but the source does not. But it works fine if we change the default cluster size to 4MB. So it has point us to the right direction. Stefan > > Otherwise, after my trivial fix, you should find cluster_size to be a > mutable concept and perhaps one that you could introduce a runtime > parameter for if you could convince the necessary parties that it's > needed in the API. > > You'd have to be careful in the case of incremental that all the various > cluster sizes work well together: > > - Granularity of bitmap (Defaults to cluster size of source, or 64K if > unknown. can be configured to be arbitrarily larger.) > - Cluster size of source file (For qcow2, defaults to 64k) > - Cluster size of target file > - Cluster size of backup routine (Currently always 64K) > > I think that LCM(source_cluster_size, target_cluster_size, > backup_cluster_size) = MAX(A, B, C) will always be a safe minimum. > > Bitmap granularity is more flexible, and it is more efficient when the > bitmap granularity matches the backup cluster size, but it can cope with > mismatches. If the bitmap is smaller or larger than the backup cluster > size, it generally means that more data that is clean is going to be > transferred across the pipe. > > (Hmm, I wonder if it's worth checking in code to adjust a bitmap > granularity after it has been created so people can easily experiment > with performance tweaking here.) > > > Let me know if any of my ramble sounds interesting :) > --John > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] drive-backup 2016-02-25 7:49 ` Stefan Priebe - Profihost AG @ 2016-02-25 7:59 ` Fam Zheng 2016-02-25 19:53 ` John Snow 1 sibling, 0 replies; 6+ messages in thread From: Fam Zheng @ 2016-02-25 7:59 UTC (permalink / raw) To: Stefan Priebe - Profihost AG Cc: Timo Grodzinski, John Snow, qemu-devel, Qemu-block On Thu, 02/25 08:49, Stefan Priebe - Profihost AG wrote: > > Am 22.02.2016 um 23:08 schrieb John Snow: > > > > > > On 02/22/2016 03:21 PM, Stefan Priebe wrote: > >> Hello, > >> > >> is there any chance or hack to work with a bigger cluster size for the > >> drive backup job? > >> > >> See: > >> http://git.qemu.org/?p=qemu.git;a=blob;f=block/backup.c;h=16105d40b193be9bb40346027bdf58e62b956a96;hb=98d2c6f2cd80afaa2dc10091f5e35a97c181e4f5 > >> > >> > >> This is very slow with ceph - may be due to the 64k block size. I would > >> like to check whether this is faster with cephs native block size of 4mb. > >> > >> Greets, > >> Stefan > >> > > > > It's hardcoded to 64K at the moment, but I am checking in a patch to > > round up the cluster size to be the bigger of (64k, > > $target_cluster_size) in order to make sure that incremental backups in > > particular never copy a fraction of a cluster. As a side-effect, the > > same round-up will happen for all modes (sync=top,none,full). > > > > If QEMU is aware of the target cluster size of 4MB, this would > > immediately jump the copy-size up to 4MB clusters for you. > > > > See: https://lists.nongnu.org/archive/html/qemu-devel/2016-02/msg02839.html > > Thanks for your patches and thanks for your great answer. But our > problem is not the target but the source ;-) The target has a local > cache and don't care about the cluster size but the source does not. > > But it works fine if we change the default cluster size to 4MB. So it > has point us to the right direction. Does it mean overriding the copy granularity is what you want to do? Asking because drive-mirror has a "granularity" parameter for this purpose, if so it should probably be considered for drive-backup as well. Fam ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] drive-backup 2016-02-25 7:49 ` Stefan Priebe - Profihost AG 2016-02-25 7:59 ` Fam Zheng @ 2016-02-25 19:53 ` John Snow 2016-02-26 8:56 ` Stefan Priebe 1 sibling, 1 reply; 6+ messages in thread From: John Snow @ 2016-02-25 19:53 UTC (permalink / raw) To: Stefan Priebe - Profihost AG, qemu-devel; +Cc: Timo Grodzinski, Qemu-block On 02/25/2016 02:49 AM, Stefan Priebe - Profihost AG wrote: > > Am 22.02.2016 um 23:08 schrieb John Snow: >> >> >> On 02/22/2016 03:21 PM, Stefan Priebe wrote: >>> Hello, >>> >>> is there any chance or hack to work with a bigger cluster size for the >>> drive backup job? >>> >>> See: >>> http://git.qemu.org/?p=qemu.git;a=blob;f=block/backup.c;h=16105d40b193be9bb40346027bdf58e62b956a96;hb=98d2c6f2cd80afaa2dc10091f5e35a97c181e4f5 >>> >>> >>> This is very slow with ceph - may be due to the 64k block size. I would >>> like to check whether this is faster with cephs native block size of 4mb. >>> >>> Greets, >>> Stefan >>> >> >> It's hardcoded to 64K at the moment, but I am checking in a patch to >> round up the cluster size to be the bigger of (64k, >> $target_cluster_size) in order to make sure that incremental backups in >> particular never copy a fraction of a cluster. As a side-effect, the >> same round-up will happen for all modes (sync=top,none,full). >> >> If QEMU is aware of the target cluster size of 4MB, this would >> immediately jump the copy-size up to 4MB clusters for you. >> >> See: https://lists.nongnu.org/archive/html/qemu-devel/2016-02/msg02839.html > > Thanks for your patches and thanks for your great answer. But our > problem is not the target but the source ;-) The target has a local > cache and don't care about the cluster size but the source does not. > > But it works fine if we change the default cluster size to 4MB. So it > has point us to the right direction. > > Stefan > Ah, sorry, I misunderstood. It's easy to change anyway! I am in favor of adding a configurable parameter, as long as it keeps the other constraints I mentioned in mind. --js >> >> Otherwise, after my trivial fix, you should find cluster_size to be a >> mutable concept and perhaps one that you could introduce a runtime >> parameter for if you could convince the necessary parties that it's >> needed in the API. >> >> You'd have to be careful in the case of incremental that all the various >> cluster sizes work well together: >> >> - Granularity of bitmap (Defaults to cluster size of source, or 64K if >> unknown. can be configured to be arbitrarily larger.) >> - Cluster size of source file (For qcow2, defaults to 64k) >> - Cluster size of target file >> - Cluster size of backup routine (Currently always 64K) >> >> I think that LCM(source_cluster_size, target_cluster_size, >> backup_cluster_size) = MAX(A, B, C) will always be a safe minimum. >> >> Bitmap granularity is more flexible, and it is more efficient when the >> bitmap granularity matches the backup cluster size, but it can cope with >> mismatches. If the bitmap is smaller or larger than the backup cluster >> size, it generally means that more data that is clean is going to be >> transferred across the pipe. >> >> (Hmm, I wonder if it's worth checking in code to adjust a bitmap >> granularity after it has been created so people can easily experiment >> with performance tweaking here.) >> >> >> Let me know if any of my ramble sounds interesting :) >> --John >> -- —js ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] drive-backup 2016-02-25 19:53 ` John Snow @ 2016-02-26 8:56 ` Stefan Priebe 0 siblings, 0 replies; 6+ messages in thread From: Stefan Priebe @ 2016-02-26 8:56 UTC (permalink / raw) To: John Snow, qemu-devel; +Cc: Timo Grodzinski, Qemu-block Am 25.02.2016 um 20:53 schrieb John Snow: > > > On 02/25/2016 02:49 AM, Stefan Priebe - Profihost AG wrote: >> >> Am 22.02.2016 um 23:08 schrieb John Snow: >>> >>> >>> On 02/22/2016 03:21 PM, Stefan Priebe wrote: >>>> Hello, >>>> >>>> is there any chance or hack to work with a bigger cluster size for the >>>> drive backup job? >>>> >>>> See: >>>> http://git.qemu.org/?p=qemu.git;a=blob;f=block/backup.c;h=16105d40b193be9bb40346027bdf58e62b956a96;hb=98d2c6f2cd80afaa2dc10091f5e35a97c181e4f5 >>>> >>>> >>>> This is very slow with ceph - may be due to the 64k block size. I would >>>> like to check whether this is faster with cephs native block size of 4mb. >>>> >>>> Greets, >>>> Stefan >>>> >>> >>> It's hardcoded to 64K at the moment, but I am checking in a patch to >>> round up the cluster size to be the bigger of (64k, >>> $target_cluster_size) in order to make sure that incremental backups in >>> particular never copy a fraction of a cluster. As a side-effect, the >>> same round-up will happen for all modes (sync=top,none,full). >>> >>> If QEMU is aware of the target cluster size of 4MB, this would >>> immediately jump the copy-size up to 4MB clusters for you. >>> >>> See: https://lists.nongnu.org/archive/html/qemu-devel/2016-02/msg02839.html >> >> Thanks for your patches and thanks for your great answer. But our >> problem is not the target but the source ;-) The target has a local >> cache and don't care about the cluster size but the source does not. >> >> But it works fine if we change the default cluster size to 4MB. So it >> has point us to the right direction. >> >> Stefan >> > > Ah, sorry, I misunderstood. > > It's easy to change anyway! I am in favor of adding a configurable > parameter, as long as it keeps the other constraints I mentioned in mind. ah great and thanks! Stefan > > --js > >>> >>> Otherwise, after my trivial fix, you should find cluster_size to be a >>> mutable concept and perhaps one that you could introduce a runtime >>> parameter for if you could convince the necessary parties that it's >>> needed in the API. >>> >>> You'd have to be careful in the case of incremental that all the various >>> cluster sizes work well together: >>> >>> - Granularity of bitmap (Defaults to cluster size of source, or 64K if >>> unknown. can be configured to be arbitrarily larger.) >>> - Cluster size of source file (For qcow2, defaults to 64k) >>> - Cluster size of target file >>> - Cluster size of backup routine (Currently always 64K) >>> >>> I think that LCM(source_cluster_size, target_cluster_size, >>> backup_cluster_size) = MAX(A, B, C) will always be a safe minimum. >>> >>> Bitmap granularity is more flexible, and it is more efficient when the >>> bitmap granularity matches the backup cluster size, but it can cope with >>> mismatches. If the bitmap is smaller or larger than the backup cluster >>> size, it generally means that more data that is clean is going to be >>> transferred across the pipe. >>> >>> (Hmm, I wonder if it's worth checking in code to adjust a bitmap >>> granularity after it has been created so people can easily experiment >>> with performance tweaking here.) >>> >>> >>> Let me know if any of my ramble sounds interesting :) >>> --John >>> > ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2016-02-26 8:55 UTC | newest] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2016-02-22 20:21 [Qemu-devel] drive-backup Stefan Priebe 2016-02-22 22:08 ` John Snow 2016-02-25 7:49 ` Stefan Priebe - Profihost AG 2016-02-25 7:59 ` Fam Zheng 2016-02-25 19:53 ` John Snow 2016-02-26 8:56 ` Stefan Priebe
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