I have found this Link http://www.principledtechnologies.com/clients/reports/Dell/PERC_H700_CacheCade.pdf on the web which shows an high performance gain for Database usage with the Dell Raid Controller Perc H700.
The key is to use a relative small SSD as a read cache for the underlying Raid System. As this idea seams good for read intensive systems it will no perform fine if you push gigs of Data into your system.
I think the SSD will be a single point of failure in the tested scenario.
Any thoughts on this ?
Based on my reading of their testing, pushing gigs of Data into the system would at worst make it perform as good/bad as it did before configuring the CacheCade drive. What really drives the performance is not merely the use of SSD as a technology, but the intelligent placement of frequently read data on the SSD as well as using the SSD as an extension of the card's onboard cache.
I agree that the SSD would be a single point of hardware failure, even in the scenario with two SSDs as there was no discussion of mirroring or allocating the drives to their own array it seemed to imply that two SSDs just presented the card with a larger SSD CacheCade volume. By the same token, the card itself is a single point of failure so I do not know if the SSD single point makes or breaks a decision based on the performance gains. At that point it really depends on your environment and requirements what other steps need to be taken to avoid those single points (e.g. clustering two servers with the same card/drive configurations, having a dedicated spare available, etc).
Thanks for pointing it out.
answered 23 May '11, 16:26
Instead of using the SSD as a cache for a larger RAID system regarding a database and the storage needs of a database system I would just go for the SSD alone. If you feel you need (R)edundancy then just use 2 SSDs in a RAID 1 configuration.
Especially if you think of the SSD just as a cache, then remeber harddisks usually have a RAM-cache of at least 8 GB (today often 32 GB). The RAID controller comes often with RAM-cache (256 or 512GB) and if a battery pack is installed it usually uses the RAM-cache also for caching writes. So with all this RAM-cache what can a "3rd Level" cache based on SSD improve?
answered 24 May '11, 03:15