It saves the backup from having to read unchanged disk blocks, compressing them and checking with the server if they are there, by only looking at some bits of memory.It seems to be very slow when doing dirty-map backups because it does the comparison.
By the way PBS works, all backups are full but only information not already on the PBS is transferred (as the same data is never stored twice). This has nothing to do with the bitmap. The dirty bitmap is only an (optional) optimization that prevents reading disk blocks (and the follow up steps of compressing and checking) that are guaranteed to already be on the PBS.You can't disable bitmap feature, or you couldn't do any incremental backup, only full backup.
My experience:Please try the following: make a backup of a running VM to PBS and then make another backup of that (still running) VM to PBS (this will use the bitmap so it does not have to read most of the virtual disk). Then Fully shutdown the VM, restart the VM (to clear the bitmap) and make another backup of that VM to PBS. If the third backup is not slower than the second, please provide timing information and logging.
Can you please explain to me what a "Live incremental backup" is? I don't understand the difference with "Dirty Bitmap".My experience:
Have tested this in my actual scenario and the dirty-bitmap, appears to be slow BUT is very quickly compared with full backup.
We have a Zimbra Mailserver VM with 1.4 TB of data, (PBS located in separate server, 1gbps dedicated network and no-specialized hardware)
-- Full backup needs aprox 20hs
-- PBS + Dirty Bitmap needs aprox 5hs
-- PBS + Live incremental backups ... aprox 5 minutes.
We are happy with these times.
Regards!
Hi!Can you please explain to me what a "Live incremental backup" is? I don't understand the difference with "Dirty Bitmap".
Set snapshot mode in backup settings. Dirty bitmaps are prematurely cleared in stop mode, so you don't get any benefit from having them.In short, what solutions do you suggest to increase the backup speed?
How does your hardware setup compare to the recommended requirements? Using a single (enterprise) HDD with ext4 or ZFS is going to be slow because of the limited random IOPS.we use snapshot but PBS backup speed is really slow.
Use ZFS and a (small but enterprise) NVMe as a special device for the metadata. The HDD does the (mostly sequential) large block storage and the NVMe does the filesystem structure (many random I/O). This is mentioned in the recommended requirements.Do not know a way to use the Single HDD with NVME cache?