Deduplication Nightmares: What to Use When TAR Slows You Down

# Deduplication Nightmares: What to Use When TAR Slows You Down If you've ever tried to push massive amounts of similar backup data into a deduplication system—say, something like Cohesity—you've probably butted heads with the limits of traditional archiving tools. For years, TAR has been the go-to format for bundling files before shipping them off to storage. But when deduplication comes into play, especially on appliances that compress and encrypt after ingest, things get messy. Real fast. A user in a popular data storage forum recently laid it out plainly: they're trying to back up thousands of OS and application binary files (SAP, Oracle, HANA—you know, the heavy hitters) using TAR, but deduplication isn't playing nice. The files aren't compressed client-side to keep deduplication possible, and they're being shipped to Cohesity via NFS. The kicker? Copying files individually is painfully slow. Like 5 hours versus 10 minutes slow. The question that emerged: Is there an archive format better than TAR when deduplication is on the table? Let's unpack that. ## The Deduplication vs. Archive Format Tug-of-War First, it's worth noting that TAR isn't inherently bad for deduplication. As some commenters pointed out, TAR is just a container—it bundles files in raw format with headers. The issue comes when you compress those TAR files. Compression obfuscates the underlying data patterns that deduplication engines rely on to detect redundancy. Same goes for encryption. So if you're TARing and gzipping (.tgz), you're basically feeding your dedup engine garbage, as far as it's concerned. The original user avoided that trap: no compression, no encryption pre-ingest. But the problem wasn't just dedup quality—it was performance. Small files slow down Cohesity's ingest pipeline over NFS. That's not surprising. Most storage systems—especially those optimized for large sequential I/O—hate being peppered with tiny file operations. Still, this leaves us with a gnarly problem. You can't copy the files one-by-one. TAR works but messes with dedup over time due to shifting content positions. What else is out there? ## Why Dedup Struggles with Changing TARs Here's the rub: every time you make a tiny change in a directory and re-TAR it, the whole structure of the resulting .tar file shifts. Because TAR is just a stream of concatenated files, the relative positions of unchanged files move. To a block-level deduplication engine, even a 1-byte shift could mean an entirely new chunk that it has to store—no dedup wins there. Some commenters referenced a 2011 paper that warned about this exact issue: TAR isn't dedup-friendly because changes ripple through the archive. But others pushed back, pointing out that modern dedup systems use smarter chunking algorithms (e.g., variable length, sliding windows) that can still find the redundancies—even inside shifted TARs. The reality probably lives somewhere in the middle. If your backup strategy involves regular updates to huge archives, you're setting yourself up for a deduplication headache. ## So What's the Alternative? Honestly? There's no silver bullet here. But there are strategies that can help depending on what you value more—restore granularity, dedup gains, or performance. ### 1. Use Chunk-Aligned Archive Tools There are a few archive tools like DAR (Disk ARchive) or Bacula that allow for chunking or segmenting backups in a more dedup-friendly way. These tools are a bit more complex than good old TAR, but they can preserve file-level context while still bundling data in a way that helps dedup engines do their job. ### 2. Split Archives Based on Content Type If you have lots of small, mostly-unchanging files (like OS binaries), group them together. The more uniform the contents of a TAR, the better deduplication tends to be—especially if files are updated at similar frequencies. ### 3. Roll Your Own Dedup-Aware Format One user hinted that TAR is still fine if you control the backup software and it understands how deduplication at the target works. That's huge. If your backup tool tracks changed blocks, aligns them with known chunks in the dedup table, and packages them accordingly, you can cheat the system a bit. Not every team has that luxury, though. ### 4. Avoid Pre-Compression or Encryption It can't be overstated: if you compress or encrypt before sending your data to the dedup target, you're torching your deduplication benefits. Some systems like Cohesity handle compression and encryption after dedup—exactly how it should be. Don't get ahead of yourself. ## "Just Use the Agent" Isn't Always the Answer Several people chimed in suggesting the Cohesity agent and scheduled jobs. Makes sense in theory: the agent can handle changed blocks, deduplication context, even handle restores cleanly. But in the real world, it's never that simple. In this case, users who own the backed-up systems need to do restores themselves—but they don't have access to the Cohesity GUI. So the team chose a scriptable approach: TAR archives stored on disk, restore via shell. Simple, fast, no GUI drama. And that's important. You can have the most elegant storage architecture in the world, but if your restore process is slow or locked behind an admin gate, users will revolt. ## A Word of Caution from the Trench One storage admin laid it bare: dedup sounds cool but rarely delivers big in the enterprise. He'd seen compression offer far more savings than deduplication, and even warned against relying too heavily on dedup due to potential chunk database issues—especially when the storage system takes a hit. That's not paranoia, it's experience. If you're building a strategy around deduplication savings, you better understand exactly what kind of files you're backing up, how often they change, and how the dedup engine works. Otherwise, you're chasing theoretical savings. ## So What Should You Do? Here's the takeaway: - **TAR isn't the villain**, but it's also not a miracle format for dedup-aware backups. - **Avoid compression and encryption pre-ingest.** Let your storage system handle that. - **Test different strategies.** Some users have had luck with split TARs, chunked archives, or tweaking the dedup settings on the storage appliance. - **Don't obsess over deduplication.** If compression gives you 50% and dedup gives you 3%, you know where the real savings are. Oh, and maybe—just maybe—it's time to rethink your archive format if restore times and dedup hits are giving you grief. The tools are out there. You've just got to pick the one that fits your pain points, not just your habit.