Adaptec maxCache(SSD Raid) + HDD Raid vs Adaptec SSD Raid 5 Deneva 2R

Question

linux

I shoveled a lot of resources, but since the solutions are new, there are very few discussions about this.

In general, there is an Adaptec 7Q Series controller that supports maxCache 3.
There are 5 OCZ Deneva 2 R disks.

The disks seem to be server ones with increased reliability, but the reputation of ssd in servers is not yet great.
In this regard, there are 2 installation options:

1) assemble Deneva 2 R SSD in Raid and make maxCache out of them and put several SAS disks in Raid 5/6 as the main array that will be cached by maxCache

2) assemble Deneva 2 R SSD in Raid 5 + 1 hot swap and hope everything goes well.

Poidee 1 option is more reliable, but it seems to me slower
Option 2 should be faster, but stops the thought of the fragility of ssd

I would like to hear your opinions.

Answer 1

If you are going to optimize for random IOPS, then only the second option (for large databases (significantly large SSD cache size), the difference is noticeable).
Regarding the reliability of the second solution, it is comparable to a large number of disks. SSDs often fly at the same time (like propellers from the same batch). More SSDs will not only increase the speed/volume, but also make the load on the SSD more uneven. And this will reduce the risk of simultaneous departure of 2 disks.
In general, the data of the raid controller uses the SSD cache quite effectively. In some, special, circumstances, the reading speed in a hybrid may be higher than in an SSD-only (very specific ones).
So both options are viable. I, personally, would fill all the slots with SSDs and not suffer.

Answer 2

With an increase in the load on the HDD, the chance of its breakdown increases. The greatest chance to take off at the disk is at the time of the array rebuild. Therefore, N + 1 redundancy systems are significantly inferior in reliability even to (Nx2) + 2. For SSD, the difference in operation, under load and without, is not so significant; the speed of access is higher (= fast rebuild), therefore the chance that another one will fly out during the rebuild is seriously lower. Especially if there is a hot spare (did I understand your option number 2 correctly?). Although if there is a hot spare, why not make RAID6?
There is another point - the SSD has a limit on the number of cell overwrites. This allows you to calculate the approximate life of the disk under a certain load. But this only makes sense if you actually plan on having a large number of writes.
In general: you need a place - put an HDD; speed - SSD. Reliability and durability depend on the type of load.

Answer 3

Adaptec knows how to hybrid Raid. In short - put ssd and hdd equally, reading only from ssd (fast), writing to both. You can collect raid 10, which will be both fast and reliable.