A question I recently asked regarding the use of enterprise 10k vs. 7.2k midline SAS disks led to some suggestions that the use of a mirrored pair of SSDs as a boot volume can make sense because:
- Prices for smaller, read-intensive SSDs suitable for boot volumes are not massively different from HDDs
- The increased I/O can be advantageous, particularly in situations such as reboots and patch installation where getting the server back up and running as quickly as possible is desirable
This led me to look into the available options a little more. I use HP kit, so my questions relate to that, but no doubt some of it is applicable across the board.
Firstly, a couple of people mentioned that HP make SSDs specifically designed for use a boot volume. Looking at the HPE SSDs data sheet, it mentions the Read Intensive SFF/LFF models as being ideally suited. Is this what people are referring to? I did see a couple of models specifically entitled "Enterprise Boot", but I'm still trying to work out whether they're an older line or not. It also mentions M.2 models, which is something I need to read into a little more.
Secondly, looking at the SSD options available for an HP DL380 Gen9 SFF chassis, I've notice that the sorts of capacities such as 80GB or 120GB that would be ideal for a boot volume are only available with a SATA interface.
As an example, a 120GB Read Intensive-3 SFF drive with a SATA interface has a list price of £195.00. When it comes to SAS, the cheapest option is a 480GB Read Intensive-3 SFF drive with a list price of £839.00. Drive capacities for SAS go as low as 200GB, but those are write-intensive or mixed-use options that are more expensive than the read-intensive 480GB drive.
As a comparison, the equivalent HDD - a 300GB 10k Enterprise SAS drive has a list price of £179.00 - very close to the 120GB SATA SSD mentioned above.
Is the lack of lower capacity/price SAS SSDs common, or is my example using a DL380 not representative of the norm? If it is, does that mean people are generally using SATA SSDs for their boot volume? Is that advisable? I've always followed the mantra of sticking to SAS because the SAS command set is supposedly more suited to a server environment, RAID, etc (I'm not expert, so admittedly I'm 'playing it safe' in the absence of knowledge of the specifics). Does using SSDs change that? Is my thinking flawed to begin with?
The HP SSDs datasheet does say a couple of things which are semi-helpful:
The SAS SSDs transfer data at full duplex (bidirectional) allowing greater I/O bandwidth to alleviate bottlenecks .... SATA SSDs are great in half-duplex (unidirectional) direct connect scenarios when lower price is a priority
... which helps explain why having a SAS interface will improve performance.
Additionally SAS uses SCSI commands for error recovery and error reporting, which have more functionality than the ATA command set used by Serial ATA (SATA).
It's difficult to when this would matter without specifics. It's something I've heard before and is one of many things I'd like to spend time understanding better.
I should say that I'm using the list prices just to allow relative comparison between products - I appreciate actual market prices would differ.