I noticed that my LTO-2 tape drive was "starving" for data and
shoe-shinning.
I was dumping to tape at 12Mb/sec and the minimum speed to prevent
shoe-shinning on an LTO-2 drive is 19Mb/sec.
So I did a check by timing a 'dd' of 10 Gb to the tape drive. It was indeed
topped at 12 Mb/sec. It took 13m51s
Now, I replaced the antedeluvian adaptec 2940 with an adaptec 29160 ultra
160 car and redid the exercice.
This time, it took 6m51s, so I was running at about 24 Mb/Sec. That was ok.
Not very fast, bot OK.
Now, when I looked at my amanda log this morning, I was very sad to see the
following:
----8<----------------------------------
STATISTICS:
Total Full Incr.
-------- -------- --------
Estimate Time (hrs:min) 0:06
Run Time (hrs:min) 2:03
Dump Time (hrs:min) 4:32 2:49 1:44
Output Size (meg) 12963.4 9414.1 3549.3
Original Size (meg) 48289.8 31693.3 16596.6
Avg Compressed Size (%) 22.5 23.1 21.4 (level:#disks ...)
Filesystems Dumped 53 12 41 (1:41)
Avg Dump Rate (k/s) 812.7 952.5 585.1
Tape Time (hrs:min) 0:13 0:08 0:05
Tape Size (meg) 12963.5 9414.2 3549.3
Tape Used (%) 6.7 4.9 1.8 (level:#disks ...)
Filesystems Taped 53 12 41 (1:41)
Avg Tp Write Rate (k/s) 17549.5 20734.5 12469.2
USAGE BY TAPE:
Label Time Size % Nb
DailySet1-018 0:13 12963M 6.7 53
-----------8<-----------------------------------------------------------------
I'm still under 20Mb/Sec
Now, I figure the problem is that when I did the "dd" test, all my holding
disk had to do is read the files. Now, it has to read the files whil amanda
is pounding at it, wrinting dump files coming from the clients... and
unfortunately, it seems my single SATA disk can't keep up with all those
I/Os
What are my options ? We can't afford to buy a beefy server just to do
backups. We are uning a centos beige commodity box. Even then, the server
seems to be I/O bound. What could I do anyway ? Buy a faster disk subsystem
? What kind of subsystem ?
Of course, I could remove the tape from the drive, and in the morning
manually run amflush, but it's not very very convenient or elegant and it
will monopolize the tape for a couple of hours in case I need to restore
something in an emergency it will be a mess.
Thanks
