[Cluster-devel] question about gfs2 multiple device support

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> Hi,
> 
> On Sat, 2023-04-22 at 09:20 +0800, Wang Yugui wrote:
> > Hi,
> > 
> > Is there some work for gfs2 multiple device support?
> > 
> Do you mean multiple devices generically, or specifically the md
> driver?
> 
> > if multiple device support,
> > 1, No need of RAID 0/1/5/6 support.
> > ?? nvme SSD is fast enough for single thread write.
> I'm not sure I understand this. Multiple device support generally means
> at least one of the RAID modes.

we can support linear mode (same as lvcreate --type linear) only firstly.

> > 2, can we limit one journal into one device?
> The filesystem always assumes a single device with one or more
> journals. If multiple devices are used, that is done at the block
> layer, which is below the filesystem layer.
> 
> > 
> > 3, can we just write lock one device, so better write throughput?
> Do you have a specific application in mind? Or certain performance
> levels that you need to hit? The write performance will depend a lot on
> the I/O pattern, and the underlying device performance. We'll need a
> bit more detail to be more specific I'm afraid,

gfs2 use 'SCSI PERSISTENT RESERVE' or similar method to lock block device
when multiple hosts access the gfs2 at the same time?

if gfs2 use multiple device directly rather than through lvm, then we 
can just lock one device rather than all device?
- journal lock one device only
- data write lock one device only.

Now SSD/SAN is very fast and become cheaper, and we can use multiple 
SSD/SAN for one bigger filesystem and bigger HPC cluster?

Best Regards
Wang Yugui (wangyugui at e16-tech.com)
2023/04/24