I stand corrected... It seems the data rate matching in LTO-3 drives isn't as flexible as I'd have thought... One interesting thing to note in the doc you mentioned is that if you think you may be shoe-shining, try backing up onto an LTO-2 tape as this will run the drive at native LTO-2 speeds rather than at the much higher data throughput of LTO-3.
Bob [EMAIL PROTECTED] wrote: > > In the message dated: Thu, 28 Feb 2008 11:21:31 EST, > The pithy ruminations from Bob Hetzel on > <Re: [Bacula-users] Volumes marked with Error> were: > => > => First a quick note... drives LTO 2nd generation and newer should not > => shoeshine unless you're really running way to slow a cpu for what else > => is going on with the computer. > > Huh? That's exactly the opposite of everything I've heard from drive > manufacturers, from Curtis Preston, etc. > > The faster the drive, the more difficult it is to supply it with enough data > to > prevent shoe-shining. In general, the limiting factor isn't the CPU of the > backup server, but the disk drives that are supplying data and the network > connection[s] end-to-end between the data source and the tape drive. > > For example, an LTO-3 drive supports a native (uncompressed) throughput of > 80MB/ > sec. This means that, for "average" data that the drive will be compressing, > the > server must supply data at the rate of 120~160MB/sec to keep the drive running > at full speed. This is not trivial. Many tape drives are capable of variable > write speeds, deliberately slowing down when the incoming data rate is > insufficient, in an attempt to avoid shoe-shining. AFAIK, the minimum data > rate > that LTO3 drives must receive in order to avoid shoe-shining is ~35MB/s. This > can be difficult to achieve in a real-world environment, such as reading data > from a server in active use, sending that data over a network (even GigE) > that's > used for other tasks, and competing with other streams of client data being > sent > the same backup media server (ie., storage director). > > My simple rule of thumb: > If the data source is a single spindle (ie. not a RAID device), then > you will not be able to feed an LTO3 drive fast enough to prevent > shoe-shining. With a single disk, even an LTO2 drive may shoe shine, > depending on the overall system and the compressibility of the data. > > > http://www.open-mag.com/features/Vol_117/LTO3/LTO3.htm > > http://www.datastor.co.nz/Datastor/Promotions.nsf/4a91ca5e06d20e15cc256ebe0002290e/d954d1c5e5e6df09cc25723b00740956/$FILE/When%20to%20Choose%20LTO3%20Tape%20Drives.pdf > > => > => If the room air temp is less than 85 degrees or so it's unlikely in a > => tape autoloader cabinet (i.e. good airflow by design) that you've got a > > Yep. > > [SNIP!] > => > => Also, have you considered spooling everything? I know this may slow > => down your backups on fast servers but the increase gained in doing more > => than one thing at a time may balance this, especially on incrementals. > > Absolutely. You may be able to avoid shoe-shining by spooling data from > individual servers onto a fast RAID device on the storage director. This will > probably produce a small decrease in the backup time for individual servers, > and a significant decrease in the aggregate backup duration for multiple > concurrent clients. > > => > => > Date: Wed, 27 Feb 2008 09:31:40 +0000 > => > From: Bob Cregan <[EMAIL PROTECTED]> > => > Subject: Re: [Bacula-users] Volumes marked with Error > => > To: bacula-users@lists.sourceforge.net > => > Message-ID: <[EMAIL PROTECTED]> > => > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > => > > => > Hi, > => > I am running the following > => > > => > Director, Storage deamon 2.2.6. The library is an Overland Arcvault 24 > => > (LTO3) > => > Most clients (about 30 ~ 8TB in total) are 2.2.4 > => > > > [SNIP!] > > => > > => > There is one thing that I thought may have a bearing. I am using a > => > mixture of spooled and non spooled backups. Some of the backups are on > => > old hardware, consist of lots of very small files (several million ~1Kb > => > html files ) and the resulting very poor throughput can result in a big > => > shoeshining problem - I generally spool these. Other ones are large > => > database files with good throughput so I run these direct to tape. The > => > spool files can be as big as 80Gb. > => > > > I have a very similar arrangement. I spool data from ~25 clients (some on > GigE > and some on 100Mb) to 3 spool files on my storage director. The spool files > are > located on separate LUNs on a fast RAID array. Each spool file is limited to > 60~90GB. > > In my case, the only client which writes to tape directly (without spooling) > is > the storage director (which is also a file server with about 3TB). I haven't > checked backup performance for "collisions" between unspooling data and a > direct backup of the sd. > > > => > The director allows four concurrent jobs, I have two tape drives one of > => > which is generally Incrementals only the other Full backups only. > => > > => > Can there be a problem if a spool file is despooling and a "direct to > => > tape" job also need to write to the tape? Should I spool all my jobs? > => > > > Hmmm.... I'm not ready to suggest that, but I am very interested in hearing > about your findings if you do try it. > > => > Any advice would be very welcome. > => > > => > Thanks > => > > => > Bob > => > > => > > ---- > Mark Bergman [EMAIL PROTECTED] 215-662-7310 > System Administrator Section of Biomedical Image Analysis > Department of Radiology University of Pennsylvania > PGP Key at: https://www.rad.upenn.edu/sbia/bergman > > > > The information contained in this e-mail message is intended only for the > personal and confidential use of the recipient(s) named above. If the reader > of this message is not the intended recipient or an agent responsible for > delivering it to the intended recipient, you are hereby notified that you > have received this document in error and that any review, dissemination, > distribution, or copying of this message is strictly prohibited. If you have > received this communication in error, please notify us immediately by e-mail, > and delete the original message. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users