Power Failure / iSCSI LUN Corruptability

iSCSI related applications
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flymeaway
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Location: Seattle

Power Failure / iSCSI LUN Corruptability

Post by flymeaway » Thu Apr 26, 2018 3:02 am

Quick question about iSCSI, power failures, and the best way to set things up.

I'm going to have a TS-877 powered by a UPS, with an iSCSI share that will be primarily accessed by an iMac connected over 1GbE but occasionally accessed by an internal virtual machine. iSCSI LYN will be one volume in a RAID 6 array.

I'd like to minimize the risk of data loss / corruption of the iSCSI LUN, but with a single UPS I can't have the software execute an orderly shutdown on the iMac. For a few reasons (not just cost, but also space and cooling constraints in my current setup) I'd like to avoid another UPS.

If the power fails, and the iMac shuts down while writing to the iSCSI LUN, do I have a high risk of data loss even if the NAS executes an orderly shutdown?

If I put the iMac on the same UPS as the NAS (it should be rated for this), what will happen if the iMac is trying to write to the target while the NAS is going through orderly shutdown? Risk of LUN corruption?

I'm thinking that a regular network share is "safer" from this perspective but I want some of the performance and other benefits associated with iSCSI.
David

Model: TS-877 R5-1600 // QTS 4.3.4.0551
Disks: 6x4TB HGST HUS726040ALE610 (RAID 6; QNAP approved) // 1x480gb Sandisk X400 SSD (no RAID; not approved)
RAM: 8gb QNAP OEM; 16gb Ballistix Sport DDR4 2400 MHz
GPU: EVGA GTX 1050 SC Gaming
UPS: CyberPower AVR1350
Cloud Backup: TBD

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dolbyman
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Location: Vancouver BC , Canada

Re: Power Failure / iSCSI LUN Corruptability

Post by dolbyman » Thu Apr 26, 2018 4:26 am

If you do not want two UPS you can do master/slave config (described in the manual) ... ISCSI is very sensitivities for sudden loss of connection .. so sudden drops of server or client should be avoided

make sure you always have backups of your LUN, so you can restore it if anything goes wrong

flymeaway
Starting out
Posts: 45
Joined: Fri Oct 06, 2017 5:02 am
Location: Seattle

Re: Power Failure / iSCSI LUN Corruptability

Post by flymeaway » Thu Apr 26, 2018 5:06 am

That master/slave config is an awesome feature I was unaware of! Thanks for the link.

Good to know re: iSCSI connection losses; I was led to believe the connection loss was a bit like suddenly unplugging a drive... It's interesting that the error exists if the client drops suddenly rather than just if the server drops.
David

Model: TS-877 R5-1600 // QTS 4.3.4.0551
Disks: 6x4TB HGST HUS726040ALE610 (RAID 6; QNAP approved) // 1x480gb Sandisk X400 SSD (no RAID; not approved)
RAM: 8gb QNAP OEM; 16gb Ballistix Sport DDR4 2400 MHz
GPU: EVGA GTX 1050 SC Gaming
UPS: CyberPower AVR1350
Cloud Backup: TBD

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