Hi Bacula community
On the search for bottlenecks in our new backup system (Bacula 5.2.10 on
Ubuntu 12.04 64bit, HP Ultrium LTO-5 drive connected by Adaptec 1045
external SAS, File pool storage on iSCSI target) I ran the "speed" tests
with "btape /dev/nst0" because the backups from local disk spool to tape
only run with 70-80 MB/s.
Block size is default 64512 bytes and I have set Maximum File Size = 8GB
so that the drive should not stop the tape too often.
Summary of the first two tests:
- Fastest zero test (4.295 GB): 178.9 MB/s
- Fastest random data test (4.295 GB): 119.3 MB/s
What I don't understand is the result of the next two tests (with bacula
block structure):
- Fastest zero test (4.294 GB): 84.21 MB/s
- Fastest random data test (4.294 GB): 81.03 MB/s
Is this normal? LTO-5 should have a speed of max. 140 MB/s with
"uncompressable" data and a speed of max. 280 MB/s with 2:1-compressable
data. Well, the test with random data gives ca. 120 MB/s I guess that's
ok, but why does the bacula structure test with random data give only
ca. 81 MB/s?
The btape "fill" test also gives 81 MB/s with an LTO-5 tape. It fills up
to 1.5 TB which is normal capacity with uncompressable random data but
the write speed is much lower than expected.
For comparison, I ran a dd test with /dev/urandom data and it shows that
the drive is capable of reaching much higher speed than with bacula:
root@bacula:/mnt/data1/tmp# dd if=urandom.raw of=/dev/nst0 bs=64k
196608+0 records in
196608+0 records out
12884901888 bytes (13 GB) copied, 112,333 s, 115 MB/s
The full btape speed test output can be found here:
http://paste.ubuntu.com/1071093/
Greets,
Mario
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