On Fri, Jul 24, 2009 at 06:48:24AM +0200, Marc Cousin wrote:
> > In theory, the latency from random IO should be much closer to zero on a
> > flash drive than on a thrashing hard drive, so I was hoping I might need
> > only 1 or two 64GB or 128GB flash drives to provide decent spool size,
> > perhaps not even raid-ed.
> >
> > In addition, SSD/flash drives should be silent and heat up the room less
> > (although that latter effect will be small--10 watts vs 2 watts for each
> > drive)
>
> For spooling/despooling there should be no latency problems. You need
> throughput more than latency, and a standard hard drive will be as good as a
> SSD or even better if setup correctly.
>
> All you really need is to be able to read and write big streams at the same
> time. So the real problem is to help your disk scheduler to be able to read
> while having a lot of data in the write cache.
>
> We managed to do that by raising the read ahead on the disk array (with the
> blockdev command in linux). We have managed to get 300MB read and write at
> the
> same time with a disk array (I admit it costed a bit more than 2 intel SSD
> drives), but we have terabytes of spool capacity.
>
> If you really want a SSD, I'd use it for the catalog's database if I were
> you.
> There, disk latency is often the main source of contention.
For spool, I would worry about the limited write (erase)
cycles of SSD. Sure, the speed of read/write is enormously
appealing, but with how much my spool gets hit I'd hate to
have to set a really early replacement schedule because my
media can't handle many writes. Rather than SSD for spool,
RAM-Disk looks like a better way to go.
-John
--
(In this one, Pinky is smart.)
Brain: Pinky, Are you pondering what I'm pondering?
Pinky: Yes I am.
-------------------------------------------------------------------
John M. Lockard | U of Michigan - School of Information
Unix and Security Admin | 1214 SI North - 1075 Beal Ave.
jlock...@umich.edu | Ann Arbor, MI 48109-2112
www.umich.edu/~jlockard | 734-615-8776 | 734-647-8045 FAX
-------------------------------------------------------------------
------------------------------------------------------------------------------
_______________________________________________
Bacula-users mailing list
Bacula-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/bacula-users
