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filesystem Archives - AWS Managed Services by Anchor

The btrfs backup experiment

By | Technical | 4 Comments

Today we’re talking about our experience with btrfs, the next-gen Linux filesystem. btrfs has been maturing rapidly over the last few years and offers many compelling features for modern systems, so we’ve been putting it through its paces on some of our backup servers. How does it stack up? Read on! We chose to test btrfs on backup servers because they can make good use of the features on offer, and the threat-level of data loss is low. For our backups, the biggest benefit comes from copy-on-write and atomic snapshots. At Anchor we use a modified version of Dirvish with support for btrfs: instead of hardlinking directories to provide historical snapshots we just use btrfs’ snapshot facility, which is very quick. Expiring old snapshots is similarly quick – it’s a…

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A crash course in Ceph, a distributed replicated clustered filesystem

By | Technical | 3 Comments

We’ve been looking at Ceph recently, it’s basically a fault-tolerant distributed clustered filesystem. If it works, that’s like a nirvana for shared storage: you have many servers, each one pitches in a few disks, and the there’s a filesystem that sits on top that visible to all servers in the cluster. If a disk fails, that’s okay too. Those are really cool features, but it turns out that Ceph is really more than just that. To borrow a phrase, Ceph is like an onion – it’s got layers. The filesystem on top is nifty, but the coolest bits are below the surface. If Ceph proves to be solid enough for use, we’ll need to train our sysadmins all about Ceph. That means pretty diagrams and explanations, which we thought would…

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100% FAT-free

By | Technical | No Comments

I wrote some documentation for our sysadmins last week detailing how one should deal with a critical diskspace notification at some ungodly hour of the morning. On the specifics of checking filesystems with the df tool: “Astute readers will notice that we don’t query btrfs filesystems here; this is because btrfs uses extents, and inodes are a non-issue.” Well, I wasn’t entirely wrong, but I wasn’t entirely right either. btrfs is a modern filesystem with lots of shiny new features. It’s definitely not production-ready yet, but like a magpie drawn to shiny things, a couple of us use btrfs on our own machines (it’s what backups are for, right?). Some time ago I wrote about how an ext filesystem can run out of free inodes and bite you. That happened…

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LCA day 2

By | Technical | No Comments

Bit of a quiet day today, the highlight was probably the presentations on btrfs and xfs. Btrfs has been developing nicely, and Avi Miller got up to spruik some of the newer features of the filesystem. A bit like ZFS (which isn’t compatible with Linux licensing terms), it pulls in a lot of smarts that are usually the domain of your RAID controller/subsystem. This means more flexibility in how you handle your data, but a lot of new complexity too. It’s exciting stuff, but we’ll be waiting a bit longer to consider it robust enough to use in production. We’d kill for the integrated snapshotting (great for backups) and data integrity checking (store CRCs with your data) features. Meanwhile, XFS reports steady progress and positions itself as the filesystem of…

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Inode shortage reaches critical levels

By | Technical | One Comment

A customer got in touch with us recently saying they couldn’t upload files via FTP due to insufficient diskspace, but there was plenty of free space apparent when they logged in and checked. We don’t normally manage their server, but we said we’d take a look. root@aria:~# touch /srv/www/newfile touch: cannot touch `/srv/www/newfile’: No space left on device After logging in and taking a look around, the problem became apparent. root@aria:~# df -h Filesystem                Size  Used Avail Use% Mounted on /dev/mapper/nayuki-root  1016M  536M  429M  56% / /dev/mapper/nayuki-usr    4.0G  1.3G  2.6G  34% /usr /dev/mapper/nayuki-var    4.0G  1.3G  2.6G  33% /var /dev/mapper/nayuki-www     50G   41G  6.4G  87% /srv/www There’s plenty of disk space… root@aria:~# df -i Filesystem                Inodes   IUsed   IFree IUse% Mounted on /dev/mapper/nayuki-root    65536    7244   58292   12% / /dev/mapper/nayuki-usr    262144   96830  165314   37%…

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