On 17/08/09, Chris Hoogendyk ([email protected]) wrote: > Cyrille Bollu wrote: > >Chris Hoogendyk wrote: > >> I wouldn't put the holding disks in raid. <snip> > http://blogs.zdnet.com/Ou/?p=484. > > While this guy is looking at things like database servers and > exchange, we ought to be able to interpret this for Amanda. A couple > of points to note for Amanda: Amanda will use all the holding disk > drives while doing parallel backups and storing output on the > holding disks. When it is writing to tape, it is constrained by the > sequential nature of the tape, and will only be doing one DLE at a > time from those that it has completed on the holding disks. Also, > Amanda's access is heavily sequential, although it may have multiple > parallel processes hitting the drives.
A slow RAID1 off two 7200 RPM SATA disks on a BBU-backed LSI hardware raid controller can do about 62031 KiB/s write and 86399 KiB/s read. Those sorts of numbers improve steadily the number of spindles you add to a RAID collection and the higher the RAID number and (in the case of writing) if cacheing is enabled. On 16/08/09, Rory Campbell-Lange ([email protected]) wrote: > On 14/08/09, Frank Smith ([email protected]) wrote: > > Chris Hoogendyk wrote: > With reference to Chris Hoogendyk's email "clarification on > parallelism", I am very curious to learn if Amanda "...still require[s] > a DLE to be completed to holding disk before it will send any of it to > tape..." In our case this is a particularly important question as, > although we can add in more AoE storage for a DLE, this will only run at > the speeds above. Do we need a 1TB SAS disk array too? >From the discussion here it seems preferable to have a DLE on two major counts. One is that compression can happen prior to writing to tape, which could result in shoe-shining, and another is that Amanda will be clearer about the amount of data it will be trying to write to a tape, in other words it will do a better fit of data to tape. The most important question I now have to ask is: How fast can a SAS-based LTO4 drive write to tape? Regards Rory -- Rory Campbell-Lange Director [email protected] Campbell-Lange Workshop www.campbell-lange.net 0207 6311 555 3 Tottenham Street London W1T 2AF Registered in England No. 04551928
