Re: [Bacula-users] Slow LTO4 write speed

2010-11-19 10:42:31
Subject: Re: [Bacula-users] Slow LTO4 write speed
From: Lukas Kolbe <l-lists AT einfachkaffee DOT de>
To: Bob Hetzel <beh AT case DOT edu>
Date: Fri, 19 Nov 2010 16:11:36 +0100
Hello Bob,

On Thu, 2010-11-18 at 16:09 -0500, Bob Hetzel wrote:
> 1) Make sure all the firmwares are up to date: the 1068E card, the tape 
> drives, specifically.  While you're at it, make sure the Adaptec card has 
> up to date firmware too.

Drives, Library, Adaptec cards have the most recent firmware; I'll look
into the LSI-controller shortly.

> 2) You might want to try this other setting too...
> Maximum File Size = 3GB

I absolutely missed the point in the documentation about writing EOFs
every X GB causing constant repositioning of the drives.

With the default of Maximum File Size = 1GB, btape and bacula do not go
faster than 60MB/s. 
I now tried several values (4, 6, 8, 12GB), and with 8GB I can reach up
to 120MB/s with btape fill on both drives. Wow. Thank you!

Where can I send the beer? Or a good scotch? :)

> 3) Looking at your output, you only got a bit over 500GB.  Are you testing 
> with an LTO-3 tape? (max uncompressed size of those is only 400GB, whereas 
> LTO-4 tapes fit 800GB uncompressed so you should have gotten much more on 
> the tape before it thought it hit the end)  If so, my understanding is that 
> the tape drive will operate backward compatibly, including lowering the max 
> read and write speeds to the previous generation's.

(I wrote the rest of the mail before playing with the maximum file size,
so this is just FYI)

Interesting. I just did another test with the second drive but the same
tapes, reaching 62MB/s and filling the tape at 770G (see below); I
suppose the tape simply wasn't rewound when I first did the test (I did
some 'speed'-tests before that could explain it). The tapes are
definitly LTO4.

> 4) Also, writing to the tape is very CPU intensive.  Is the system  busy 
> doing something else?

No, the system was otherwise completely idle (no VMs, no other bacula
processes running, no DB).

> Just a few shots in the dark there, hopefully one of them helps.

Very much appreciated, thank you. 

> In addition, until you get everything working, you should probably not mess 
> with the default network buffer size.  The manual has this to say about 
> that setting:
> Maximum Network Buffer Size = bytes
> where bytes specifies the initial network buffer size to use with the File 
> daemon. This size will be adjusted down if it is too large until it is 
> accepted by the OS. Please use care in setting this value since if it is 
> too large, it will be trimmed by 512 bytes until the OS is happy, which may 
> require a large number of system calls. The default value is 32,768 bytes.
> The default size was chosen to be relatively large but not too big in the 
> case that you are transmitting data over Internet. It is clear that on a 
> high speed local network, you can increase this number and improve 
> performance. For example, some users have found that if you use a value of 
> 65,536 bytes they get five to ten times the throughput. Larger values for 
> most users don't seem to improve performance. If you are interested in 
> improving your backup speeds, this is definitely a place to experiment. You 
> will probably also want to make the corresponding change in each of your 
> File daemons conf files.

Thanks for the pointer; I did it after desperatly trying random things a
while ago; it is removed for now.

kind regards,

Beautiful is writing same markup. Internet Explorer 9 supports
standards for HTML5, CSS3, SVG 1.1,  ECMAScript5, and DOM L2 & L3.
Spend less time writing and  rewriting code and more time creating great
experiences on the web. Be a part of the beta today
Bacula-users mailing list
Bacula-users AT lists.sourceforge DOT net

<Prev in Thread] Current Thread [Next in Thread>