Hello, my setup is a Supermicro A1SAM-2750F with a LSI 9240-8i as SAS HBA. My primary goal is to use the 24-Bay Box as a Storage NAS. Since the board is pretty capable with 8 cores and 4 NICs,...
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Hello, my setup is a Supermicro A1SAM-2750F with a LSI 9240-8i as SAS HBA. My primary goal is to use the 24-Bay Box as a Storage NAS. Since the board is pretty capable with 8 cores and 4 NICs, I might decide to add some other VMs later on. Currently I have 2x Samsung 840 EVO 250GB SSDs and 6 4TB WD Red drives attached directly to the LSI 9240 via SF8087 using 2 rows of the chassi's backplanes. I wanted to use the SSDs in a Raid-1 mirror configuration for the ESXi system and VM Storage. The 4 TB drives get directly mapped via RDM into the OpenMediaVault VM to build a Linux MD-Raid6. The card has the latest Firmware and I installed the latest VMWare LSI driver package, storcli etc. I set it all up and basically everything works. The 4 TB WD drives perform stellar with write speeds >100MB/s using GBit Ethernet. However the SSD-Raid-1 doesn't perform very well at all. I only get write speeds @10-15 MB/s. This is both true for write tests using the ESXi 5.5 ssh-shell and writing into the VMDK of my fileserver via the guest OS. I also tested the same setup with two HP 2.5" 10k SAS drives - same speed at 10-15 MB/s. I did this to rule out a compatibility issue with the SSDs, although they are listed as compatible for my LSI card. Off course I did some researching and googling. As it turns out the 9240 does not have any cache memory what makes the device really slow in Raid-5 configurations. Apprently this is also true for Raid-1. So I went a step further. I removed the Raid-1 configuration and booted the disk as a JBOD single drive setup. The speed however did not improve. So I deactivated the controller's BIOS which resulted in not being able to boot from the 9240-card. So I connected the SSD directly to a SATA3 port of the Intel chipset on the Mainboard. After booting the box I got really good speeds on the SSD @250MB/s from within the guest OS. The HP SAS-Drive which is still connected to the 9240 with it's BIOS disabled still only delivers 10-15MB/s. A very popular explanation is, that ESXi does no host side caching and fully relies on the controller's "write back" capabilities. Since my card has no cache it has no write back and thus the performance is bad. However the onboard SATA3 controller should suffer from the very same issue! I can't imagine that an Intel AHCI controller has built in caching... I might just order a 9261-8i which does native Raid-6 and has a cache, but I'm actually more interested in solving this strange issue... Any ideas? regards, Fabian