linux-ext4 - Re: [LSF/MM TOPIC] - SMR Modifications to EXT4 (and other generic file systems)

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Message-ID: <CAB-428=Mx8kqym601rHvdbvYkWMbdKYtoJJuAV0EN1U5JU23Mw@mail.gmail.com>
Date:	Sun, 15 Feb 2015 14:27:20 -0600
From:	Alireza Haghdoost <haghdoost@...il.com>
To:	Adrian Palmer <adrian.palmer@...gate.com>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	ext4 development <linux-ext4@...r.kernel.org>,
	Linux Filesystem Development List 
	<linux-fsdevel@...r.kernel.org>
Subject: Re: [LSF/MM TOPIC] - SMR Modifications to EXT4 (and other generic
 file systems)

>> I think one of the important design decisions that needs to be made
>> early on is whether it is possible to directly access some storage
>> that can be updated with small random writes (either a separate flash
>> LUN on the device, or a section of the disk that is formatted for 4kB
>> sectors without SMR write requirements).
>
> This would be nice, but I looking more generally to what I call
> 'single disk' systems.  Several more complicated FSs use a separate
> flash drive for this purpose, but ext4 expects 1 vdev, and thus only
> one type of media (agnostic).  We have hybrid HDD that have flash on
> them, but the lba space isn't separate, so the FS or the DM couldn't
> very easily treat them as 2 devices.
>

Adrian,
What if vdev that has been exposed to ext4 composed out of md device
instead of regular block device ? In other words, how do you see that
these changes in EXT4 file system apply on software RAID array of SMR
drives ?

--Alireza
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