Re: [Networker] Upgrade to LTO4 library, opinions about these libraries

On 21/02/2009, at 03:36 , Goslin, Paul wrote:

I wonder...
Are those speeds measured in a pristine lab environment with thedrives idle ? Or in a real-world setting when the drives are allpumping data @ max data rates when fast robotics are actuallyneeded....
A more important number to know/measure/reveal would be whatpercentage of those 'implemented' units are still in use a year ortwo after being installed. And of those units that have beenreplaced, what were they replaced with ? (I'd bet it was not anotherSL500)
The one users experience of having to replace the robotics 8 timesin 2 years definitely points to a serious design flaw and/or verypoor materials choice for physically stressed parts.... Or maybe hejust got a lemon ?
I think the best measure of performance for a tape library / silo isthe trial by fire method and/or the long term experience of themajority of the users who work with them on a daily basis...
Kind of like autos, Toyota touts the very high percentage ofCorrolas ever sold still on the road being driven daily... That's areal-world, experience based statistic that is difficult to counter...

Libraries that are designed to work in rack spaces I believe arealways going to be slower than their standalone counterparts. Someonequoted the L700 as being a fast library, but going back a littlefurther I think it was hard to beat, for a standalone non-silolibrary, the speed of the 9710/Timberwolf.

With any modular library, a key aspect to reliability is how well it'sbeen put together. When joins have to be fussed over to a <3mmvariance, it means that if someone just slaps it together because it'sFriday afternoon and they want to go home soon, that's possibly goingto impact production usefulness.

I've got a variety of customers using SL500's, and they're notreporting failure rates that are in excess of other types oflibraries. I hate to suggest it, but someone who has had the roboticsreplaced 8 times in 2 years sounds like either they've received alemon or the people doing the replacements aren't paying enoughattention to the quality of the build in a modular system --- or both.

That being said, I'm pleased to see there's this sort of discussion onthe list - too often people worry about the speed and capacity of themedia, and forget about the incidental factors, such as roboticmovement times and even load/seek time on the media. These can play animportant factor in backup and - more importantly, really - recoveryschedules. When it comes to measuring backup performance, the sequenceof "returning to slot, picking next tape, placing in drive" canactually start to make a significant impact on what I refer to as yourovernight "backup bandwidth". If it takes say, 70 seconds for onelibrary to do it and your drives write at 160MB/s, then that's a 10GBinterruption to your backups. If another library can do the same thingin 30 seconds, that's just a 4.7GB interruption to your backups. (I'mdeliberately excluding load/unload times of the media, because in arealistic comparison it would be the same drives in bothlibraries...) Repeat that say, 30 times a night, and suddenly you'redeciding whether you can afford to lose 300GB in backup time a nightor 141GB in backup time a night. For bigger sites, these numbers canactually become very important.


Cheers,

Preston.

--
Preston de Guise


"Enterprise Systems Backup and Recovery: A Corporate Insurance Policy":

http://www.amazon.com/Enterprise-Systems-Backup-Recovery-Corporate/dp/1420076396

http://www.enterprisesystemsbackup.com

NetWorker blog:

http://nsrd.wordpress.com

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Re: [Networker] Upgrade to LTO4 library, opinions about these libraries ?