Re: Serious performance issues with mdadm RAID-5 partition exported through LIO (iSCSI)

On Sep 18, 2012, at 8:37 AM, Ferry wrote:

As I'm not sure where to go, I've
sent this to both linux-raid and target-devel lists.

I think you're better off taking a chance with one, waiting a few days, then going with another, rather than crossposting.

So for example I see disk <sdX> do 600-700kB/s reading in I/O stat
whilst it's writing about 100kB/s.

You've provided no information on the hardware being used, version of kernel and mdadm, or info on the array such as mdadm -Evv <array>.

With msdos partitions I could easily mess with it myself. GPT however
also has mirror headers and those might actually overwrite my data if
done incorrectly. At least - that's what I'm worried about, not sure if
that theory is solid.

GPT contains checksums for the header and table, so you can't just make manual table edits. And there's no need, just use gdisk (a.k.a. GPT fdisk) or sgdisk.

Also, with msdos I could easily make backups with
dd or sfdisk (of the partition table). Not aware of such a tool for gpt.
Parted doesn't seem to be able to dump them.

gdisk (interactive) or sgdisk (command line) can do this.

Chris Murphy