Alexander Leidinger

Just another weblog

Oct
30

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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