Eric Bollengier wrote: > Le Friday 07 November 2008 14:36:46 Kern Sibbald, vous avez écrit : >> On Friday 07 November 2008 13:19:45 Ralf Gross wrote: >>> Kern Sibbald schrieb: >>>> On Thursday 06 November 2008 22:47:41 Ralf Gross wrote: >>>>> Alex Chekholko schrieb: >>>>>> On Wed, 5 Nov 2008 16:12:51 +0100 >>>>>> >>>>>> Kern Sibbald <[EMAIL PROTECTED]> wrote: >>>>>>> For writing to tape (providing it is LTO-n) I strongly recommend >>>>>>> a block size not to exceed 256K. >>>>>> Hi Kern, >>>>>> >>>>>> Why do you say that? Is this thread relevant?: >>>>>> http://www.mail-archive.com/[EMAIL PROTECTED]/msg0 >>>>>> 12 46.h tml >>>>>> >>>>>> Also, I would like to corroborate the OP's experiences; I had an >>>>>> almost identical thread about small block size and slow write >>>>>> speed: http://www.nabble.com/LTO-4-performance--td17407840.html >>>>>> >>>>>> In fact, I was unable to get higher block sizes working at all with >>>>>> btape: >>>>>> http://www.adsm.org/lists/html/Bacula-users/2008-05/msg00504.html >>>>>> >>>>>> So I am still stuck at ~22MB/s writing to LTO-4 with the default >>>>>> block size. >>>>> I don't think that the blocksize is the problem. I did some tests but >>>>> couldn't get higher results with larger blocksizes. I get 75-85 MB/s >>>>> with the default bs and no additional tuning. >>>> That is probably correct, but most likely only because you have a >>>> bottleneck elsewhere -- probably in one of the points I mentioned. The >>>> speed is always capped by the slowest component. Once you remove the >>>> other bottlenecks on your system, the blocksize will very likely become >>>> the bottleneck and then you can measure the difference. >>> I didn't want to compain, just show the org. poster that his 22 MB/s >>> are likely not a bs issue. >>> >>> That being said, I started a thread on the user list a while ago where >>> I aked what throughput people are getting when writing to tape. Nobody >>> involved in this thread got higher numbers than 80-85 MB/s for a >>> single job. >> That is probably reasonable for one job, but if you are writing to an >> LTO-2,3, or 4, we know that with multiple simultaneous jobs it is possible >> to get write speeds of 150 MB/sec. >> >> Kern > > This is with a good hardware compression rate, but it's a very good test, > IMHO, more than using random data to get only 80MB/sec. If you able to write > at 150MB/s, i'm pretty sure that you will be able to write at 80MB/s... Even > if your source file is made with a dd if=/dev/zero, your harddisk, your > network, your SCSI/SAS or whatever controler have to handle it like real > data. > >
I've done extensive throughput experiments on my Dell LTO4 and have never managed to get the advertised streaming-rate of 120MBytes/sec. Even writing a stream ov zeros to the drive with hardware-compression turned on only gets me 100MBytes/sec. All zeros without compression: [root]# mt -f /dev/st0 compression 0 [root]# dd if=/dev/zero of=/dev/nst0 bs=1000000 count=10000 10000000000 bytes (10 GB) copied, 107.498 seconds, 93.0 MB/s All zeros with compression: [root]# mt -f /dev/st0 compression 1 [root]# dd if=/dev/zero of=/dev/nst0 bs=1000000 count=10000 10000000000 bytes (10 GB) copied, 100.147 seconds, 99.9 MB/s gzip for comparison: On a 1.6GHz Xeon box: [root]# dd if=/dev/zero bs=1000000 count=10000 | gzip -c | wc -c 10000000000 bytes (10 GB) copied, 135.79 seconds, 73.6 MB/s gives a compression ratio of 1030:1 And on a 2.9GHz Xeon box: [root]# dd if=/dev/zero bs=1000000 count=10000 | gzip -c | wc -c 10000000000 bytes (10 GB) copied, 76.6102 seconds, 131 MB/s Cheers, Terry ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
