On 2015-05-19 10:43 AM, Dimitri Maziuk wrote:
> On 05/19/2015 11:42 AM, Bryn Hughes wrote:
> ...
>> recent LTO versions (5/6) you really need to make sure your disk setup
>> on your backup storage server is capable of keeping up with the tape
>> drive - most consumer hard drives top out at about 120MB/sec for
>> sequential reads and much less than that for random I/O (such as having
>> backup jobs writing to the disk at the same time as the tape drive is
>> reading from it)
> Wow these seagate nas drives must be magic then: it's 120MB/s sequential
> read yet I get consistent 340MB/s sustained writes
>
>> 11-May 23:00 starfish-sd JobId 13: Despooling elapsed time = 00:02:24, 
>> Transfer rate = 345.8 M Bytes/second
> ...
>> 12-May 12:30 starfish-sd JobId 13: Despooling elapsed time = 00:02:25, 
>> Transfer rate = 343.4 M Bytes/second
> ...
>> 14-May 03:33 starfish-sd JobId 34: Despooling elapsed time = 00:02:27, 
>> Transfer rate = 338.8 M Bytes/second
> ...
>> 18-May 19:49 starfish-sd JobId 57: Despooling elapsed time = 00:02:26, 
>> Transfer rate = 341.1 M Bytes/second
> and so on. On software raid-5-ish (raidz1) with lz4 compression at
> filesystem level.

You realize that using a RAIDZ with LZ4 compression is going to give far 
better sequential performance than a single stand alone drive would with 
uncompressed data, right?  ZFS RAIDZ volumes are perfect for sequential 
read/writes though they are still IOP limited.

There's no magic.  You have an appropriate configuration for what you're 
doing, exactly what I was intending to convey to the individual looking 
to build a brand new backup system.  Try running straight EXT4 on a 
single drive with jobs spooling to the drive while it tries to feed an 
LTO5 drive and let's see if you can sustain anywhere close to 
100MB/sec.  Hint: you can't.

My Bacula SD box has 5 old WD 'green' 1.5TB drives (5400 RPM) in a 
RAIDZ1 setup.  Works great.

>
> How about you iostat that LTO 5/6 drive while a restore job is reading
> from it and a backup job is writing at the same time and then post speed
> comparisons?
>

You can't run both a restore and a backup to a tape device at the same 
time. Tape doesn't work like that.

Bryn


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