I just wanted to drop a note to the list with my experience.
I've been using Amanda since around 2005 with 3 Amanda servers originally with AIT5, then transitioned to LTO6 and now to LTO7 on one server (still LTO6 on the other 2). During that time, disk storage on two of these servers has escalated almost exponentially. The AIT5 was 400GB native and seemed capacious. Server disk drives had gotten as big as 300G, but we still had many smaller drives. Then we started seeing drives in the 1TB, 2TB and then 4TB range, and setting up multiple RAID arrays with these. We transitioned to LTO6 on all three servers (Sony dropped out of the competition and AIT died). More recently we started seeing 6TB and 10TB drives. We now have arrays of 10TB drives on two servers, and have added a new library with two LTO7 drives on one server. The other department is struggling with costs. We have nearly 100TB total disk capacity on each of these two servers now.
One of the issues I have been dealing with is how long it takes Amanda to do the backups. With the LTO6, and doing about 2.5TB compressed backups each night on a 7 day backup cycle, it was not uncommon for the backups to run over 24 hours. I took to checking on it around the time the next run was to start in the late evening and making a considered decision whether to do an amcleanup -k so that the next run could start, e.g. sacrifice one or two DLEs to get a fresh run that would include all of the DLEs. Typically, when looking at the runs with top, I would see multiple gzips occupying CPU time. I understand that I could use pigz, but these are multi-purpose servers, and I didn't want to dominate the CPUs even more. The situation was becoming almost untenable, and disk space was escalating all the time.
I've now had a bit of time running with LTO7, Amanda 3.4.5, and letting the tape drive do hardware compression. It happens that I (and some others on the list) couldn't figure out how to turn off compression on the LTO7, but I was already motivated to try running with hardware compression. I'm now routinely getting anywhere from 5TB to 8TB of uncompressed data (a substantial portion of it is uncompressible, e.g. large TIFFs), and it is often completing in about 8-10 hours without affecting the server load during the work day. I'm using two 4TB SSDs for holding space, and I'm using include and exclude to keep DLEs to no more than about 900GB, though many are smaller. I had previously aimed at staying under 500GB and shooting for 200 to 300GB for DLEs. I've converted all the dumptypes that I'm using to application am-gtar with compress none. I set the size of the LTO7 to ~12TB in the tapetype definition, and I set the maxdumpsize parameter to ~15TB. Everything is finally running quite smoothly.
With a 48 slot library and two LTO7 drives, I'm also ready for some additional growth. I'm seeing top speeds of about 230MB/s for tape writes, which is much faster than the top rating for LTO6, but not up to the top rating for LTO7 of 300MB/s. I had previously gotten up in the 150s for LTO6 which has a top rating of 160MB/s. I'm not sure where the bottleneck is for the LTO7. The library is running off a SAS HBA separate from the SAS HBA for the external disk cabinets. However, tape writing is not a bottleneck for my backups overall, so it's not a big deal.
The basic point here is that I've cut away from my long time thinking that it is better to do software compression so that Amanda's planner knows how much tape space is actually being used. While it feels a little uncomfortable not knowing how well the compression is working, it was always a heuristic that end of tape is how you know the tape is full. If it seemed like too little data was written, then you assumed tape errors, shoe shining, or some other issue. So, it's not really that different, and now it's much faster.
-- --------------- Chris Hoogendyk - O__ ---- Systems Administrator c/ /'_ --- Biology & Geosciences Departments (*) \(*) -- 315 Morrill Science Center ~~~~~~~~~~ - University of Massachusetts, Amherst <[email protected]> --------------- Erdös 4
