Rudolf Cejka wrote:
Keith Brautigam wrote (2006/02/15):
Quinton Jansen wrote:
What speeds are others getting when using an LTO-3 drive?
I take up interest just in direct writing speed to the tape reported
by iostat, which I have typically about 60-80 MB/s, but still I think
that it should be better, because 80 MB/s is native speed of LTO-3 drives
without compression, so with compression it should be possible to go
above 100 MB/s (look for example at
http://h18006.www1.hp.com/products/quickspecs/11739_div/11739_div.html).
What actual speed are you getting now during the de-spooling process?
Also, how would you recommend measuring how fast you are writing to the
tape (I realize you're on FreeBSD not Linux)? I'm new to having such a
fast drive and am also interested in in creasing write performance.
If I'm reading the numbers correctly, 2GB in 13 minutes (10GB/hour) is way
too slow (should be around 200G/hour).
From bacula report? There is a problem, that there are counted all times,
like data spooling and attributes despooling (I suppose, that you do use
spooling, because it is almost a "must" for LTO-3 drive).
Feb 15 00:39:23 localhost kernel: scsi0 : Adaptec AIC79XX PCI-X SCSI HBA
DRIVER, Rev 1.3.11
Feb 15 00:39:23 localhost kernel: <Adaptec 29320ALP Ultra320 SCSI
adapter>
Feb 15 00:39:23 localhost kernel: aic7901: Ultra320 Wide Channel
A, SCSI Id=7, PCI-X 67-100Mhz, 512 SCBs
It would be interesting to see the real agreed communication speed,
beause I still have problem to run LTO-3 drive from HP with Adaptec
using 320 MB/s (it is known bug). It works just with 160 MB/s, so I had
to buy LSILogic, which does work with my LTO-3 over 320 MB/s very well.
However, I did not get any speed differences :o(
My dedicated bacula server is a dual Athlon MP 2GzH system with 4 SATA
drives (add-in non-RAID 4 port Promise controller) and a Gig NIC running
Linux Ubuntu 5.10. I have the same version of bacula, and it is also
compiled from source.
FreeBSD 6.0-STABLE, dual Intel Xeon 3.6 GHz, spooling is on
3ware 9500 with 7 drive RAID-0.
How did you arrive at using hardware RAID and seven drives? Was that
convenient with your hardware, or did you first try a smaller number of
drives (like I have) and find they were not enough?
The main performance enhancement for me was switching to a system with
more CPU power. The second most important performance enhancement was
how I configured the systems four drives, so as to not be disk I/O bound
This is what I already said before: Bacula has and will have more and
more performance problems with high speed backup cofigurations. MD5 checksums
should be either precomputed before writing data to the tape, or maybe
there would help two writing threads instead of just one: One thread
would read data and compute md5, the second thread would just try to
write data to the tape.
(although that's still the slows part of the system). Two of the drives
are configured with software RAID1 for the OS etc. The other two (250GB
each) are configured as software RAID0 with XFS, and serve as a
dedicated data spool for bacula. I also spool attributes so that data
entry into the catalog does not slow writing to the tape.
The second problem is that there can be just one spooling area, where one
read + write RAID array may have performance problems even in very good
configuration. There would be good to have some possibility to say, that
spooling area is exclusively reserved for despooling process (or atleast
more independent spooling areas, some reservation feature, ...).
not sure). I believe the advertised speed for LTO3 is around 60 MB/sec,
80 MB/s
but I think seeing a 44 MB/sec average in real world performance (on a
relatively old and cheap server) is pretty decent.
However for LTO-3 it is not very satisfactory, because minimal physical
speed accomodation for LTO-3 drives is 27 MB/s (HP) or 40 MB/s (IBM),
so 44 MB/s is the lowver bound for IBM drives for best effectivity.
It would be interesting to see, how many repositions is done during
write. There is one value in HP drives (Repositions Per 100 MB), which
can help in performance diagnostics. And I think that there are even
better counters in IBM drives.
How do you find/set the number of repositions? What other sorts of
tuning did you perform on the drive?
Also, I'm using an older SCSI controller card (160 not 320) and have
never tried to tune the drive with mt or any other utility.
My experiences are not so good among 160 MB/s and 320 MB/s - I have
the same performance in both cases for now.
So it sounds like I should be okay with an older Adaptec 160 MB/s card?
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