Alexander Leidinger

Just another weblog


Local backup vs. tarsnap

A lot of peo­ple do not do back­ups at home. Unfor­tu­nately this includes me. So far I was lucky that noth­ing bad hap­pened (or that I was able to get back all via manip­u­lat­ing on-disk-data by hand). For me this is mostly because of the price and com­plex­ity (num­ber of backup media involved) for local back­ups. It also means that I only need a backup for the case of a disk–crash, not because I need to recover a file because I acci­dently deleted it (yes, I am very good at not loos­ing data at home… maybe this is also the rea­son why I have so much data).

I have about 1 TB of raw disk space at home (two times raidz1). Not all of this needs a backup (or is used at all), for exam­ple the base sys­tem files, /usr/local, the ports dis­t­files and pack­ages all do not need a backup, but my cam­era fotos (cur­rently 8 GB) should be included in a backup, my home should be included in a backup, my local stag­ing area for the con­tent of my web­server should be included in a backup, my mails (cur­rently 800 MB) should be included in the backup, local patches to FreeBSD should be included in the backup, …

So let us cal­cu­late with about 200 GB of more (mails, fotos, pri­vate videos) or less (MP3s from my own CDs) impor­tant data for a full backup. Most of it will not change often (MP3s, pri­vate videos, fotos), so once a month should be ok, and some (e.g. my mails) change daily, so an incre­men­tal each day and a full once a week would be inter­est­ing for me. When I do such a backup, I do not want to shuf­fle around tapes a lot. Maybe one or two times (s0 2 – 3 tapes) would be ok. So I am talk­ing about 80 – 200 GB per tape. The prices for this range from 700 EUR to 1300 EUR just for the tape drive. I have also seen a tape drive from Iomega for about 400 EUR (120 GB per tape), but some­how this sounds like a not so trust­worty solu­tion to me (I do not know why, it is just a feel­ing, maybe I am a lit­tle bit biased because of the high-end solu­tion at work, if some­one knows more about those Iomega dri­ves and tapes in a long term or high-useage envi­ron­ment, please write a comment).

When I take the cur­rent price of tarsnap into account, I come to about $60 per month for the stor­age, and again $60 for the ini­tial trans­fer of 200 GB. This assumes the 200 GB are not very com­press­able. With each incre­men­tal backup (changed files mat­ter, not a diff between the files), I assume about 10 GB per month of change (= $3 per month). Yes, this is most prob­a­bly too much, but I try to cal­cu­late a worst case sce­nario. So this sums up to $60 once and $63 per month. I do not take into account my too slow upstream band­with. When I assume a 1500 EUR tape drive plus tapes plus clean­ing car­tridge, we are talk­ing about some­thing like 2 – 3 years of stor­ing the backup in tarsnap (with the Iomega drive this would be just one year).

When I assume that I over­es­ti­mated every­thing with a fac­tor of 2, this means 5 – 6 years of using tarsnap vs. buy­ing an expen­sive tape drive. Now the ques­tion is, will the tape drive sur­vive this long, will I be able to use such a drive in new hard­ware  in 6 years, will tarsnap sur­vive this long, and will it stay at the same or bet­ter price level (this is also influ­enced by the price of the stor­age provider).

Another solu­tion would be to go with a mixed set­ting, e.g. an 1 TB hard-disk (less than 150 EUR  for the hard-disk (with 7 years war­ranty) and an exter­nal case) to do the long term stor­age of high-volume but long-term–sta­ble stuff (fotos, videos, music), and use tarsnap for the low-volume fast chang­ing stuff (con­fig files, mails). This way the amount of money for the really impor­tant things is not much, I would expect less than 1 GB com­pressed (= less than an EUR per month). This also sounds like a solu­tion which allows me to be lazy (the impor­tant stuff can be auto­mated, the nice to have stuff can be done from time to time as needed).

I think I should ask Collin if he has a way to receive SWIFT (IBAN/BIC) trans­fers for tarsnap…


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