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I'm looking at the DELL PowerEdge™ R720 from Hetzner.

This server has a Dell PERC H710 8 Port SAS/SATA 6GBit/s raid controller.

I have the choice between:

  • 3 x 600GB SSD (MLC SATA 3Gb/sec)
  • 6 x 600GB 15k rpm SAS disks

The price between both options are the same.

I need at least 1,2 TB of disk space, more is better.

The server will be used to host ESX 5 development machines. Mostly heavy reads, not that many writes.

Which option would be more performant?

With the 6 x 600GB SAS disks I would also have the possibility to put them in RAID 10 (and of course RAID 5). With the SSD's it will be RAID 5.

rept
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2 Answers2

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RAID 10 is better for databases. Even though you'll be heavier on reads, caching and changes to the actual database will still impact the performance of your server.

I would go with the 6x SAN disks. SSDs in RAID 5 is just asking for trouble since you only have a single drive tolerance, and SSDs tend to fail rather suddenly where spinning drives tend to have warning signs.

Nathan C
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Based on the information in your question, it is impossible to say for sure, which option is best. It depends on the specifics of your workload and priorities besides performance. My best guess, from the information, that you provide would be, that the SSD option would outperform the SAS spinning disks. However, RAID-5 has a number of issues, that you should consider, before settling on that version, especially: 1: RAID-5 is quite vulnerable to critical data loss, if a second disk fail during a RAID rebuild. 2: during a RAID rebuild, the system will perform very poor, due to the load of the rebuild. 3: RAID-5 cause write-amplification, where everytime you write user data to your drives, parity must also be written, causing a higher number of total writes, and thus shortening the lifespan of your SSDs.

Simon Kepp Nielsen
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