esxi 5.1u1, mb with 2xsata3 ports, want add SSD cache but which port?

[fsora]

Good morning to everyone,

this is my first post and i'm not english-speaking, so i'll try to explain my question in the best way.

We are running esxi 5.1u1 on a small server with desktop components:

- i5-3570k                                        [could get i5-3570 non-K]

- z77 motherboard (msi g43)             [could get Q77 board from gigabyte] 

- 16gb ram ddr3 1600mhz non-ecc

- 2xHDD western digital RED 2TB each, non-raid

- backup on NAS

and about 10vm between linux and windows hosts (usually only 6 are up for normal production[AD, FS, PBX), to manage a network of 4 workstations.

We are wondering to add a 120gbSATA3 SSD as caching, using build-in feature of ESXI 5.1u1, but we have a problem on choosing the correct disk configuration since we got only 2 sata3 ports.

1. HDDs are sata3 and actually connected to the 2 sata3 ports (intel controller);
2. we got other 4 sata2 ports on different build in controller;
3. we can't afford a raid card at the moment;
4. should we put the ssd on sata2 to benefit the cache speed, or the only way is sata3?

Thanks in advance.

[JarryG · Accepted solution]

You can put SSD on sata2 (interface is backward compatible), but you will suffer serious performance penalty. With sata3 you get 600MB/s transfer speed, with sata2 just 300MB/s (taking into account 8b/10b encoding). And sequencial transfer speed of today's consumer SSDs is approaching even that maximum limit of sata3 interface (i.e. Samsung 840Pro: 520/540 MB/s). If you put SSD onto sata2, you will seriously degrade its performance, maybe to half of its capability. If you want to use SSD for caching, I would not recommend putting SSD on sata2 interface.

I'd suggest to put HDD on sata2 instead (and use sata3-port for SSD). With exception of disk-cache, no common hard-drive has transfer speed higher than 300MB/s. It might suffer a little performance degradation too while using cache, but sure not as much as SSD...