On 12/3/2014 8:12 AM, Daniel Pocock wrote:
> Can anybody make any practical comments on how to choose a suitable
> spool disk (both speed, size and whether to make an array of disks for
> spooling)?
>
> It would be useful to see some examples of spooling for LTO-3 up to
> LTO-6 and also any comments about things to avoid
>
> For example, if somebody uses LTO-3 (400GB, supporting 60 - 80MB/sec)
> will a single SSD sustain the necessary speed de-spooling to tape or
> should multiple SSDs be used in RAID0 or RAID1?  Is it feasible for
> clients to be spooling more jobs to the same disk simultaneously while
> the tape drive is reading from it?

A single SSD such as the Intel Fultondale series will sustain average 
read speeds far in excess of the LTO-6 400 MB/s maximum. A Lyndonville 
series will sustain average read speeds of around 200 MB/s. But you have 
to compare apples to apples. The maximum write speed of LTO-6 is 400 
MB/s, but what is the average write speed after writing many blocks for 
a whole job? A single Lyndonville drive may suffice, or a RAID array of 
SAS drives. I stay away from RAIDing SSDs and won't use RAID0 for anything.

Also, in addition to de-spooling data to tape, it must also de-spool 
metadata to the database. IMO, the SSD makes far more difference for the 
database than for the spool.


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