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Just installed a LSI 9750-8i to my old system with Windows 8.1, added two 2TB disks to SAS-0 port, created RAID1 with them, assigned a letter E: and started cloning data to it. Is it possible to add more disks to LSI's RAID1 without destroying the data on the disks, or I must start over? Documentation is not clear enough about this operation

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  • Just an observation - I think you may be asking the wrong question. I suspect you want to turn your RAID1 into a RAID10 array. Adding more disks to a RAID1 array does not give you more space, it gives you more copies if the same data. RAID10 creates a RAID1 array of typically 2 RAID0 arrays.
    – davidgo
    May 2, 2020 at 19:29
  • I want to be sure if I can add more disks to already active RAID1 array on this specific controller, and if possible the data on the first two disks stays intact
    – 1000Gbps
    May 2, 2020 at 22:53
  • We are talking past each other. If you want more useable space by adding an additional 2 or more disks you need to change from RAID1 to RAID10 (and you might get better answers by looking at how to convert RAID1 to RAID10)
    – davidgo
    May 2, 2020 at 23:25
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    The only link I could find would imply you need to destroy and rebuild :( - reddit.com/r/sysadmin/comments/2tz1zs/…
    – davidgo
    May 2, 2020 at 23:30
  • So again transfering data between machines for another 5-6 hours ... That's sad :(
    – 1000Gbps
    May 3, 2020 at 16:22

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You cannot "add more disks" to a RAID 1 configuration to extend the available disk space. RAID 1 in a simple sense is a data copy between the disks. You can't add a 3rd disk and maintain a RAID 1.

If you're looking to add a single disk to extend total storage, you should be looking at RAID 5 or 6. But those have a higher minimum disk requirement. It comes down to how many disks you are willing to use and what the end goal of your utilization of your RAID is.

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  • What I understood is that expanding RAID1 with more disks means increasing mirrors and read speeds
    – 1000Gbps
    May 3, 2020 at 16:21
  • Technically you can have as many disks as you want in a RAID 1, but you would gain nothing except a little more redundancy. Each disk contains an exact copy of all the data that exists. That is why you see RAID 1 using only 2 drives the majority of the time. If you are adding mirrors, then you are looking at RAID 10 (minimum of 4 disks). You pair 2 disks in a RAID 0 for performance, then RAID 1 that pair for redundancy. Please review this to get a better understanding of RAIDs: en.wikipedia.org/wiki/Standard_RAID_levels
    – Sorean
    May 3, 2020 at 17:20
  • Already read it - the interesting thing is that RAID 1+0 or RAID 10 is the opposite of your RAID 10 explanation. It's RAID1 mirrored on RAID0, not vise versa
    – 1000Gbps
    May 3, 2020 at 18:15
  • Fair enough, I mixed it up early in the morning. But the answer is still the same based on your question.
    – Sorean
    May 3, 2020 at 22:14
  • As OP I never wrote extending the available disk space. But already got an answer from local sysadmin group - those controllers support a lot of drives in RAID1 mode, depending of how much SAS ports are available on the board
    – 1000Gbps
    May 6, 2020 at 16:26

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