Thinking about setting-up as distributed RAID array over iSCSI. Has anyone else tried this, if so what was your experience.
To be more specific I am thinking of a couple of CentOS servers each with say four drives, all published as iSCSI targets. Then one Windows Server accessing all of these via iSCSI and connecting those targets together to create a software RAID array.
One of my concerns is the rebuild time if one of those servers is offline for a short amount of time. Would it then be necessary to rebuild the entire array from scratch or is software RAID clever enough to only rewrite sectors that have changed? My concern being that a small network glitch could otherwise potentially cause a long rebuild process.
Thanks,
Nick
Best Answer
This has many drawbacks and not a single advantage I can see, so I don't understand why you would want to do this.
Any outage of the iSCSI connection will likely require a full RAID rebuild. The RAID subsystem doesn't know that the disc is the same if it sees it again and that it is more or less unaffected, but even if that would be the case, it doesn't keep a log of write operations since the failure that it could use to bring the drive up to date again.
The network connection will be a serious bottleneck, especially in case of a rebuild. You will have a small number (likely just one) 1 GBit/s network connections compared to multiple SATA/SAS connections with up to 6 GBit/s each, connected over the PCIe bus.
This whole setup is really delicate and easy to bring to a complete halt.