Re: Extraction time of small file from big-ish archive

2014-10-29 21:44 GMT+01:00 Colin Percival <cperciva@tarsnap.com>:

On 10/29/14 11:44, Elvis Stansvik wrote:
> I just signed up for Tarsnap and I'm very pleased with the service. It's a
> weight off my shoulders to finally have both my laptop and my small FreeBSD
> server backed up somewhere. Many thanks to Colin for the nice design of the
> system and the simple tar-like interface.

:-)

> Short question: When extracting a small (few KB) file from a somewhat big
> archive (15 GB or so, with quite a number of files), what is it that takes
> time? For me it took ~4-5 minutes to get such a file out.
>
> It's not a problem at all since this is something I hope to never have to do,
> but I was just curious what is the actual bottleneck. I'm guessing it's the
> downloading, decryption and scanning of the tar header?

You're exactly right. Tarsnap stores the tar headers separately from the tar
data in order to speed up this process, but there's still ~50-100 bytes (512
bytes of tar header, compressed) which needs to be downloaded per file so that
tarsnap can decide which parts of the archive need to be extracted.

Alright. Makes sense. Thanks for the quick answer.

Elvis

--
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid