Thanks Neil. I tried setting my sda7 partition to generate write
errors every 40 bytes(writing 1 byte at a time). I did :
1. Create a array with:
mdadm -C /dev/md/me0 -l faulty -n1 /dev/sda7
After this step I can see /dev/md127 and when i do a mdadm -D /dev/md127, i get:
/dev/md127:
Version : 1.2
Creation Time : Wed Sep 28 17:35:50 2011
Raid Level : faulty
Array Size : 969410424 (924.50 GiB 992.68 GB)
Raid Devices : 1
Total Devices : 1
Persistence : Superblock is persistent
Update Time : Wed Sep 28 17:35:50 2011
State : clean
Active Devices : 1
Working Devices : 1
Failed Devices : 0
Spare Devices : 0
Name : eng-dev16.lab.local:me0 (local to host eng-dev16.lab.local)
UUID : 96f4be10:312f9574:f40107aa:d9f278ba
Events : 0
Number Major Minor RaidDevice State
0 8 7 0 active sync /dev/sda7
2. Set write fault level with:
mdadm -G /dev/md/me0 --layout=wp40
After this when i write > 40 bytes into /dev/md127, i dont get any
I/O errors. I am sure i am doing something wrong here.
Any help is much appreciated.
Thanks
Jojy
On Wed, Sep 28, 2011 at 4:11 PM, NeilBrown <neilb@xxxxxxx> wrote:
> On Wed, 28 Sep 2011 12:48:37 -0700 Jojy Varghese <jojy.varghese@xxxxxxxxx>
> wrote:
>
>> Hi
>> I am trying to dynamically add error injection to my virtual
>> disk(LVM) for testing+ debugging purpose. I saw "faulty" personality
>> module in the kernel and was wondering if there was any documentation
>> on its usage. I am not looking to set up a RAID but a simple mapped
>> device. So the basic use case is that I need to be able to dynamically
>> add/remove error sectors and also be able to have granular error
>> configuration like read error, read+write error etc.
>>
>> thanks in advance
>> Jojy
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>
> The 'faulty' md personality is described briefly in the 'md.4' man page which
> is included in the mdadm distribution.
> I've included the relevant part below.
>
> Configuring the type of faults is described in mdadm.8 under the '-p
> --layout=' section. So can adjust the settings using mdadm --grow.
> so:
> mdadm -B /dev/md0 -l faulty -n1 /dev/sda
>
> will build a 'faulty' device which provides access to /dev/sda, but
> introduces faults. Initially no faults will be introduces.
>
> mdadm -G /dev/md0 --layout=rt400
>
> will tell md0 to generate a read error every 400 requests, but not to
> remember the error - rt == readtransient
> --layout=rp400
> will create a persistent error every 400 reads subsequent reads of the same
> block will produce the same error. at most 50 persistent errors can be
> recorded.
> mdadm -G /dev/md0 --layout=clear
> will stop producing new errors
> mdadm -G /dev/md0 --layout=flush
> will forget all persistent errors.
>
>
> from md.4:
>
> FAULTY
> The FAULTY md module is provided for testing purposes. A faulty array
> has exactly one component device and is normally assembled without a
> superblock, so the md array created provides direct access to all of
> the data in the component device.
>
> The FAULTY module may be requested to simulate faults to allow testing
> of other md levels or of filesystems. Faults can be chosen to trigger
> on read requests or write requests, and can be transient (a subsequent
> read/write at the address will probably succeed) or persistent (subse-
> quent read/write of the same address will fail). Further, read faults
> can be "fixable" meaning that they persist until a write request at the
> same address.
>
> Fault types can be requested with a period. In this case, the fault
> will recur repeatedly after the given number of requests of the rele-
> vant type. For example if persistent read faults have a period of 100,
> then every 100th read request would generate a fault, and the faulty
> sector would be recorded so that subsequent reads on that sector would
> also fail.
>
> There is a limit to the number of faulty sectors that are remembered.
> Faults generated after this limit is exhausted are treated as tran-
> sient.
>
> The list of faulty sectors can be flushed, and the active list of fail-
> ure modes can be cleared.
>
>
> from mdadm.8:
>
> When setting the failure mode for level faulty, the options are:
> write-transient, wt, read-transient, rt, write-persistent, wp,
> read-persistent, rp, write-all, read-fixable, rf, clear, flush,
> none.
>
> Each failure mode can be followed by a number, which is used as
> a period between fault generation. Without a number, the fault
> is generated once on the first relevant request. With a number,
> the fault will be generated after that many requests, and will
> continue to be generated every time the period elapses.
>
> Multiple failure modes can be current simultaneously by using
> the --grow option to set subsequent failure modes.
>
> "clear" or "none" will remove any pending or periodic failure
> modes, and "flush" will clear any persistent faults.
>
>
>
> NeilBrown
>
>
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