On Tue, Aug 08, 2006 at 10:27:00AM -0500, Frank Smith wrote: > Jon LaBadie wrote: > > On Mon, Aug 07, 2006 at 02:37:17PM -0400, Ian Turner wrote: > >> Marilyn, > >> > >> Amanda's tape selection policy is as follows. > >> > >> Consider the set of tapes T. We can partition the set into two disjoint > >> subsets A (the set of active tapes) and I (the set of inactive tapes). > >> Assuming I is nonempty, there exists a subset P of I, called the set of > >> preferred tapes. Note that T = A + I, and P is a weak subset of I. > >> > >> Amanda will only use tapes from I; active tapes are not considered for > >> overwriting. Also, tapes from P are preferred to other tapes in I; a tape > >> not > >> in P (but in I) will be used only if no tapes in P are available. If no > >> tapes > >> from I are available, then no tapes are used and Amanda will go into > >> degraded > >> mode. > >> > >> Tapes are assigned to each of the two sets as follows: > >> -- Any labeled but unused tapes are in I and P. This includes unlabeled > >> tapes > >> if the label_new_tapes option is set. > >> -- The most recently used "tapecycle" number of tapes is in A. > >> -- Any remaining tapes are in I. The single least recently used of these > >> is > >> also in P. > >> > >> This algorithm is applied from scratch any time a new tape is needed > >> during a > >> backup run. You can run the algorithm without running Amanda by doing > >> 'amtape > >> taper'. > >> > >> What all of this means from a slightly less mathematical perspective is > >> that > >> Amanda will not consider overwriting the tapecycle most recent tapes. If > >> you > >> want to relax this restruction, just reduce tapecycle, and Amanda will > >> countenance the use of newer (more recently used) tapes. > >> > >> Alternatively, if you have a specific tape that you want Amanda to reuse, > >> just > >> relabel it, and it will be treated as a new tape. > >> > >> --Ian > >> > >> On Monday 07 August 2006 13:10, HUGHES Marilyn F wrote: > >>> We have a situation where the next Amanda tapes that it is asking for > >>> are currently offsite. It costs $75 for them to be retrieved so we > >>> don't want to do that. > >>> > >>> > >>> Besides we have available tapes here onsite. Is there a way (a command > >>> or other way?) to force Amanda to select one of the tapes that we have > >>> onsite? Does Amanda select from the top of the tapelist on down? > > > > > > Ian, > > > > Thanks for your description. I was thinking of trying to put together > > a description of the tape selection algorithm myself. But I didn't > > know some(most?) of the detail. Certainly not in mathematical sets. > > > > One thing still up in the air (to me anyway) is final tape selection > > from within the tapelist and physical tape changer. Your description > > gets to which tapes are "eligible" to be selected, but not which tape > > (or runtape number of tapes) among that set is ultimately chosen. > > > > Let me try to use my own terminology to descibe your algorithm so > > that I'm sure I understand it. I'd appreciate corrections to any > > mis-statements, in fact or in timing. And, perhaps you could extend > > it by describing the final tape selection. > > > > From the entire tapelist, those marked "no-reuse" are eliminated > > from further consideration. Only those marked "reuse" are considered. > > (is there any other tapelist classification?) > > > > The reuse"able" list is divided into "previously used" and "never used" > > (have a valid date stamp or have a 0 date stamp respectively). > > > > The previously used tapes are date-sorted and the most recently used > > tapecycle-1 of those are eliminated from further consideration. This > > would be your "active" set that are reusable but can't be overwritten > > at this time as they fall within a tapecycle's number of tapes. > > > > Any remaining, previously used tapes, plus the labeled but never used > > tapes (if any), constitute the set of tapes eligible to be used for > > the next run. > > > > If what I've described is reasonably accurate, none of it is dependent > > on tapelist order nor availability in the tape changer. So the physical > > device must be accessed before the final selection of a tape to use. > > > > Does amanda at this point look specifically for the next tape based on > > the order in the tapelist file? (i.e. the last tape in the tapelist > > file that is on the eligible list) Will it scan the entire changer > > looking for that specific tape? Or will it start to scan the changer > > looking for any tape from the eligible list? Or something else? > > > > Thanks. > > > > jl > If Amanda's behavior hasn't changed (I'm still using 2.4.5), it will > use the first non-active tape it finds in the changer. It appears > to just load the next tape until it finds a non-active one, not look > for an unused one or find the oldest. >
>From this discussion, your and my observations also, it appears the order of tapes listed in the tapelist file is immaterial. Anyone disagree? -- Jon H. LaBadie [EMAIL PROTECTED] JG Computing 4455 Province Line Road (609) 252-0159 Princeton, NJ 08540-4322 (609) 683-7220 (fax)
