On Thu, Jun 7, 2012 at 7:29 AM, Nick Daly
What's Tahoe's required overhead? Is it static (5KB, regardless of partition size), or does it grow with the reserved space (2% from 0 - 5 GB, 3% for > 5GB)?
Hm, I'm not exactly sure. In general, people tend to allocate large amounts of disk space to one Tahoe-LAFS storage server, like at least 0.5 TB, and then not worry about the few KB or MB of overhead that Tahoe-LAFS adds. The storage server process is the one that stores ciphertext on disk and sends and receives ciphertext over TCP on behalf of a storage client. It stores each piece of ciphertext in a separate file in its local filesystem, and it organizes those files into 2-level hierarchy of directories. That's a source of overhead, since it takes a little more than X bytes of disk space to store an X byte file in your file system. That overhead is proportional to the number of files stored and the exact amount is determined by the filesystem, but I would estimate 2 KiB per file. Another source of overhead is that the storage server maintains a couple of small files of metadata about which files it has processed. That is a small fixed amount that doesn't grow with the number or size of files. It's probably around 10 KB. Another source of overhead is per-file metadata -- leases (markings showing that someone said "I'm interested in this file -- please don't garbage-collect it for at least 30 more days!"), and integrity-checking hashes. The integrity checks are proportional to the size of each file, but small. It's about 64 bytes of hashes for each 40 KB of file.
My biggest concern with this is space, as the 2GB microSD card the DreamPlug comes with is tough to manage. If we can use the SD card slot when it's available, this'll be less of a problem, but I haven't really thought about that problem yet.
My instinct would be not to try to make use of such scarce storage resources, but instead say "Want to contribute to the great FreedomBox Cloud Storage grid? Then plug in a 1 TB hard drive to the USB port!". That would actually make the resulting storage much more reliable, because only people who felt a certain level of willingness to contribute would run a Tahoe-LAFS storage server at all. By excluding all the people who turned it on at some point and then got bored a few hours later and turned it off again, we would greatly reduce the churn and unreliability. Regards, Zooko _______________________________________________ Freedombox-discuss mailing list Freedombox-discuss@lists.alioth.debian.org http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/freedombox-discuss ----- End forwarded message ----- -- Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org ______________________________________________________________ ICBM: 48.07100, 11.36820 http://www.ativel.com http://postbiota.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE