Re: Large no.of extents for a single small file with a fresh RAID5 setup

["Lakshmipathi.G" <lakshmipathi.g@giis.co.in>]

> 
> >I'm using Ubuntu(16.04) desktop version (not server) running Xorg and others. May be its possible its
> >flushing data to disk at constant time. If you like to give it a try again with servers, below is the
> >exact script along with its timing & multiextent output.
> 
> Archlinux here, with my btrfs vm and browser and music player, still one
> extent.
> 
looks like I have better setup to produce single-extent files than yours :-)
> Are you under heavy memory usage?
> 
no, not as per top and free. 'top' shows mem.usage as:
KiB Mem :  7092516 total,  5961796 free,   794836 used,   335884 buff/cache

where 'compiz' process uses around 2.5% of memory and 'free' command reports
almost 5gb as free. May be some 'sysctl' or others needs to be adjusted on my setup?
> >
> >one more curious thing, is it fine to have extents with size 4096 on RAID5 setup?
> >
> 
> Sure, why not?
> 
> Any size aligned to sector size is valid, no matter the profile.
> 
> For 4K extent, RAID5/6 will do read-modify-write, which is very common.
> 
> Thanks,
> Qu
> 
While looking into mapping from logical->physical chunks on RAID5. I was wondering 
how these 4KB extents will fit into 64KB data-stripe?

I didn't have idea about read-modify-write, just found few wiki links on it, will 
check. thanks

Cheers.
Lakshmipathi.G