That’s because the backup app needs to reassemble all those individually backed-up blocks into the current representation of the file, and the more of those there are, the longer it will take the backup servers to provide your file.įor these reasons, Backblaze also excludes VM image files and other large file types (it also doesn’t back up system files or applications), as you can see in the app’s Exclusions screen. On the restore side of the equation, if you’ve been backing up a large VM image for months, with changes happening regularly, and then you need to restore it, you’ll hit another performance problem.However, as Yev pointed out, the resources necessary to analyze all the blocks in a multi-gigabyte file are significant-you need enough drive space to store a copy of the file, and then the backup app has to spend a lot more time and CPU power analyzing all those blocks. It might seem as though large files wouldn’t present a problem after initial backup as long as they didn’t change all that much. After the initial upload, apps like Backblaze and CrashPlan do block-level data deduplication, which means that they analyze small blocks of each file, compare them to what’s already backed up, and copy only those blocks that are new or changed.That’s to be expected, of course, but what people may not realize is that smaller files can be blocked from uploading during that time, leaving them unprotected. On initial backup or when a lot of data changes, large files take a long time to upload.Yev Pusin, Backblaze’s Director of Marketing, explained that Code42 wasn’t just making an obvious statement about smaller archive sizes improving performance for a few reasons: I was curious about Code42’s performance claims, however, so I checked with CrashPlan competitor Backblaze (which has sponsored TidBITS in the recent past). TidBITS member Peter Erbland said, “It seems like it is defeating the purpose of an offsite cloud backup in case of a catastrophic loss of data.” Needless to say, Code42’s announcement perturbed some users, who notified us of the change. Seriously? Code42 is actually admitting that CrashPlan may not back up large files correctly? Isn’t that Job #1 for any backup app? We have always recommended you not include applications or large files in your selection as they may not backup correctly. More troubling is the comment earlier on in the note, which says: That’s obvious, no? If you eliminate large files from a backup, everything will run faster (and Code42 won’t need to add storage as quickly).
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