From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Linux mdadm superblock question. Date: Tue, 16 Feb 2010 12:24:20 -0500 Message-ID: <4B7AD4C4.4090209@tmr.com> References: <20100216115036.0f6b7bb6@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100216115036.0f6b7bb6@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Justin Piszcz , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > On Thu, 11 Feb 2010 18:00:23 -0500 (EST) > Justin Piszcz wrote: > > >> Hi, >> >> I may be converting a host to ext4 and was curious, is 0.90 still the only >> superblock version for mdadm/raid-1 that you can boot from without having >> to create an initrd/etc? >> >> Are there any benefits to using a superblock > 0.90 for a raid-1 boot >> volume < 2TB? >> > > The only noticeable differences that I can think of are: > 1/ If you reboot during recovery of a spare, then 0.90 will restart the > recovery at the start, while 1.x will restart from where it was up to. > 2/ The /sys/class/block/mdXX/md/dev-YYY/errors counter is reset on each > re-assembly with 0.90, but is preserved across stop/start with 1.x > 3/ If your partition starts on a multiple of 64K from the start of the > device and is the last partition and contains 0.90 metadata, then > mdadm can get confused by it. > Given that 4k sector drives make that a lot more likely that it used to be, I suspect some effort will be needed to address this sooner or later. > 4/ If you move the devices to a host with a different arch and different > byte-ordering, then extra effort will be needed to see the array for > 0.90, but not for 1.x > > I suspect none of these is a big issue. > > It is likely that future extensions will only be supported on 1.x metadata. > For example I hope to add support for storing a bad-block list, so that a > read error during recovery will only be fatal for that block, not the whole > recovery process. This is unlikely ever to be supported on 0.90. However > it may not be possible to hot-enable it on 1.x either, depending on how much > space has been reserved for extra metadata, so there is no guarantee that > using 1.x now makes you future-proof. > > And yes, 0.90 is still the only superblock version that supports in-kernel > autodetect, and I have no intention of adding in-kernel autodetect for any > other version. > -- Bill Davidsen "We can't solve today's problems by using the same thinking we used in creating them." - Einstein