I have bought two Intel DC S4500 480 SSDs (comes with 5 year warranty) to use with a HP G7 DL360 1U Server in RAID1. Unfortunately after purchasing the disks, I figured out that the integrated P410i RAID Controller supports 6Gbps SAS but not 6Gbps SATA.
These SSDs got 500MB/s sequential read but with 3Gbps interface that is limited to ~300MB/s. I also have a couple of 6Gbps SAS Drives (old - has no warranty/reliability as new one). Now my question is which will perform better for a web app hosting/KVM virtualization environment:
(a) 2 SSDs in RAID 1 (with 3Gbps interfaces) or 2 SAS 10k Drives in RAID 1 (with 6Gbps interfaces) and why?
(b) Also, compared to 2 x 6Gbps SSDs in RAID1, how much is 2 x 3Gbps SSDs in RAID1 performance noticeable?
Answer
In most scenarios, including common virtualization workloads, the SSDs will outperform the HDD drives due to lower latency and higher IOPS.
The link speed is a lot less relevant than latency or IOPS in most real world workloads, so I guess the difference is not too big. If you want actual numbers, you'll have to perform a benchmark with your workloads as this really varies greatly depending on your specific setup. The link speed will be most relevant for large I/O operations, e.g. copying large files.
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