From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: raid0: "clean" state on drive failure/removal Date: Sat, 28 Feb 2015 08:56:25 +1100 Message-ID: <20150228085625.7377171a@notabene.brown> References: Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/wRw9wSarWNX2ZNr838y_juk"; protocol="application/pgp-signature" Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Sushma Gurram Cc: "linux-raid@vger.kernel.org" List-Id: linux-raid.ids --Sig_/wRw9wSarWNX2ZNr838y_juk Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 27 Feb 2015 20:54:32 +0000 Sushma Gurram wrote: > Hi, >=20 > A basic question on raid0 behavior. >=20 > When a drive fails/removed in a raid0 array, =E2=80=9Cmdadm =E2=80=93deta= il=E2=80=9D reports the array > state as clean instead of failed. >=20 > It appears that the drive is whacked out of the array, but that array slot > continues to show =E2=80=9Cactive sync=E2=80=9D state. >=20 > I/O to the failed drive errors out. However, it appears that I/O to other= drives > in the raid0 array would succeed. How would the user know about the array= state > and potential data loss? Should the array information be cached, drive > failure/removals be monitored and checked against the cached information? The user would know about potential data loss in *exactly* they same way as if half the sectors on a single hard-drive stopped working. i.e. the filesystem would complain. >=20 > Could anyone please explain the reason for this behavior of not reporting= a > raid0 array as failed? RAID0 is not really RAID - there is no redundancy. So it isn't treated like RAID. RAID0 is simply a mapping off linear addresses onto multiple devices. There is no sense in which the array as a whole "fails", or any value in marking a device as "failed". If there is something wrong, then IO requests will fail. Not necessarily a= ll IO requests, but some. Just like a normal drive that has partially failed. NeilBrown >=20 > Thanks, > Sushma >=20 > ________________________________ >=20 > PLEASE NOTE: The information contained in this electronic mail message is= intended only for the use of the designated recipient(s) named above. If t= he reader of this message is not the intended recipient, you are hereby not= ified that you have received this message in error and that any review, dis= semination, distribution, or copying of this message is strictly prohibited= . If you have received this communication in error, please notify the sende= r by telephone or e-mail (as shown above) immediately and destroy any and a= ll copies of this message in your possession (whether hard copies or electr= onically stored copies). >=20 > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html --Sig_/wRw9wSarWNX2ZNr838y_juk Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIVAwUBVPDoCTnsnt1WYoG5AQIVrRAAltOYL8WCqSug6qoiYZegTdxW2jwjVYXR cBn0KyBW1NqlKbbxwQpqlX9jsfwvPkAyAg6dHGy1AfM7tXcqWBaBjSHlBzR5XbfY HNN2pTvrEz8YBQ7R963A0j6y/JoXO2NPe6J9FiQ7gLca10VPuA8XXCCRAgRU+QJg zaRYWGWfV4IWvb0B7UeZ78HTgwC4pyhgOWqmawQS31OpalZ+4lMjmp/cXg1/ONDY Uar7BuJm3/wkY80F5TnVgj1WsE59tccaBPdvW1ultlx97NR93fq+XnWY2SalJY+k KRq4c4bXv7ydzcjq1gm+ht35Rp8I6OS+j/aYyjHodldL0qNeVzX/BlqrS+KlRutO vnodJZtmHodGMHb4LF32vgyQHs+KuL1pVGzThKnMlGoh7Cn8stV5qhyMJouBEUWv rMJE/679Di8JLVm1kAR+fBhBpAY7pJ2mDxL/1MozKHoZawSc0buapobYedrYaD1E AiuGvHD7NSiR+syhRttRSlVo4YjtLbK1sX57Ry3kTd+uXKi7CZfejgdrVhuOcTHq w/0IXwe1VAM3draj2DYl26qd9yA7BhqGTP0gfuH17epAdyGUiP6rLQP52KF5Crpl 3uecxovU7McpIGprkazOHrHW0xKNehzkUq47AYZsK8I4zUCBSwkM348JJ5M5bQqL DGqrAc9gNbI= =l1Z/ -----END PGP SIGNATURE----- --Sig_/wRw9wSarWNX2ZNr838y_juk--