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Large Hyper-V incremental backups

I'm currently running backup exec 2014 and backup up (amongst other things) a hyper-v host with 6 VMs. I have a full backup every other weekend and incrementals every weekday. I changed around our backup scheme recently to make it a bit more fault tolerant, most notably redirecting each backup to it's own storage. When I did this, I noticed that the backup sizes for my incremental backups reported by backup exec for my hyper-v host did not match the actual backup sizes being used on disk, not even close to.

When backup exec finishes it's incremental backup of my hyper-v host, it reports backup sizes that are anywhere from about 1.5 GB to 5 GB depending on what was done that day. If I look at the log for the job, the sizes for each hyper-V host are consistent with that number, showing backup sizes for each host that are typically well under 1 GB before compression, and compression rations between 2:1 and 3:1. However, when I actually go and look at the NAS and the files that BE has created, the size of the vhdx files it creates are all in excess of a 1 GB, commonly 2-3 GB, resulting in the actual size of the hyper-V host incremental backups being about between 10-20 gigs a day. Knowing what's on most of those servers, typically things like a windows 2012 install running nothing but a DHCP server, the backup sizes reported by backup exec are accurate to what the size of the backups should be... so then why are the actual an order of magnitude larger than that?

I'm currently experimenting with using the "Microsoft Incremental Backup" method to reduce the backup sizes, but even if it works to reduce the backup sizes this is unadvised as it requires all of my VMs to permanently run in checkpoint mode and checkpoint mode isn't even supported for some types of servers per microsoft documentation (you're not supposed to run a DC in checkpoint mode, or at least you're not supposed to use checkpoints to rollback a domain controller). If I can't find a good method of dealing with this, I may ultimately have to treat all of my virtual servers as physical servers for the purposes of hyper-V and just back them all up individually to get thse backup sizes down to an appropriate size.

Btw, the reason the size is an issue is because of copying the backups offsite. We have plenty of storage space and network bandwidth onsite, but our internet bandwidth is limited and we're already pushing closer to this limit than I'm really comfortable with.

Is this an issue that only I'm seeing, in which case I may have a configuration error somewhere, or is this normal behavior for hyper-v backups? Is there a method that I can get these backups down to the correct size? There's really no reason for most of these backups to be even 1 GB, let alone multiple GBs.

2 Replies

So, after enabling the

So, after enabling the "microsoft incremental backups" the backup sizes are substantially smaller than they previously were, but still on an order of magnitude larger than they should be. Microsoft incremental backups are confirmed being used in the logs. (The line "Microsoft incremental backups will be performed." now appears under backup set detail information) and the reported size of the backup in the log remains unchanged at about 78 MB. (current log shows 78,171,751 bytes, previous log shows 71,236,990 bytes)

The actually space used for the avhd files for the current backup is 662 MB, the previous backup was 1.57 GB. I'm thinking I'm gonna run a test of backing up the server as though it were a physical machine to a temporary directory to see how much space it's full and, more importantly, it's incremental backup uses.

So... backing up my virtual

So... backing up my virtual server as a physical machine has resulted in a backup that is only 350 MB, down now from the average of probaby about 1.5 GB. I have noticed that it appears that when I switched over to running microsoft incremental backups, the backup set display now properly displays the actual size of the backups (previously it always displayed 13 GB for this particular server, regardless of actual amount of data backed up). Oddly, the incremental backup done using the microsoft incremental method last night clocked in at 4.37 GB for some reason.

I wish I knew why, I suspect some odity between backing up the server both as a physical and virtual machine at the same time. If I got and look at the snapshot by viewing the backup sets associated with the virtual server, it unfortunately shows all of the backups as full snapshots, so I have no way of determining what 4.6 GB changed that I can find.


Right now, I'm trying to find a compelling reason to continue backing up my virtual servers through the host, it simply seems much more effective in almost every fashion to back them up as physical servers. There's a fairly minor increase to the management complexity in that I have to add all of the servers to a backup job (or create a seperate backup job for each one), but I'm saving gigs and gigs of data, both in the full backup and in daily incrementals by backing them up as though they were physical servers.