[lug] Reliable SATA server?

[Lee Woodworth]

On 05/08/12 13:30, Rob Nagler wrote:
>> A data point for you.
> 
> Many thanks.  That's very interesting.
> 
>>    time tar --bzip2 --one-file-system -cpf /mnt/backup/root_fs.tar.bz2 /
> [...]
>>    only one core is ever active and is pegged at 100%
> 
> Are there processes waiting on disk?  Seems like you'd have three
> processes: read, compress, write.  Would be good to test against a
> pipeline to see if the performance improved.

For time tar --bzip2 --one-file-system -cpf /mnt/backup/root_fs.tar.bz2 /

    real    6m48.727s
    user    6m46.781s
    sys     0m8.057s

There are two processes: tar (1.0%) and bzip2 (99.0%) effectively running
on one core. Neither iostat -d 1 nor vmstat -d show any reads, but the
buffer cache is at 13,346,872MB and the root fs is only 2,391,376MB.
Doing this after a cold boot would probably show reads happening.

Given that the source and destination are on different spindles,
I don't expect the reads to make much of a difference for this
example -- 2.4GB is compressing down to 772MB (3.1 : 1).

The 'average' write rate is 1.9MB/s so all the tar process needs to do
is average 5.9MB/s while reading to be balanced with the bzip2 process.
Reading 10MB/s on a different spindle should be trivial, even with lots of
small files.


For time tar --one-file-system -cpf - / |
         (time bzip2 > /mnt/backup/root_fs2.tar.bz2)

    real    6m54.672s
    user    6m51.562s
    sys     0m3.064s

    real    6m54.673s
    user    6m52.330s
    sys     0m8.753s


There are still just two processes, tar (1.0%) and bzip2 (99%) on one core.
No reads, occasional burst writes of usually about 30-50MB in 1 second.


For time tar --gzip --one-file-system -cpf /mnt/backup/root_fs.tar.gz /

    real    1m52.148s
    user    1m51.607s
    sys     0m5.012s

Two processes, tar (~3%) and gzip (99%) over two cores.
No reads, ocassional burst writes of 130MB/s to 190MB/s
over one second (probably reflecting drive cache fill
speed -- 64MB cache on the disks). Compression is from
2.4GB to 856MB (2.8 : 1).

> 
> Rob
> _______________________________________________
> Web Page:  http://lug.boulder.co.us
> Mailing List: http://lists.lug.boulder.co.us/mailman/listinfo/lug
> Join us on IRC: irc.hackingsociety.org port=6667 channel=#hackingsociety