RAID0 with bitmap support in 2.6.15 kernel

Hi Folks,

I am creating RAID0 with bitmap support in 2.6.15 kernel.

For that I have created 10GB partition each on 4 sata disks and try to
created RAID0 over these 4 10 GB partitions and use one of the partitions on
one of the disks for keeping the bitmap file. I have use following command
for creating RAID0.

# mdadm -Cv /dev/md0 -bitmap=/root/mntbitmap/RAID0.bitmap -bitmap-chunk=2048
-l0 -n4 /dev/sd{a1,b1,c1,d1}

But after this I am getting Segmentation fault and kernel oops as shown in
dmesg.

# dmesg

[ 2419.835895] md: raid0 personality registered as nr 2
[ 2419.836176] md0: bitmap file is out of date (0 < 1) -- forcing full
recovery
[ 2419.836191] ----------- [cut here ] --------- [please bite here ]
---------
[ 2419.881887] Kernel BUG at drivers/md/bitmap.c:1592
[ 2419.913287] invalid operand: 0000 [1] SMP
[ 2419.940119] CPU 1
[ 2419.953249] Modules linked in: raid0 ipv6 parport_pc lp parport autofs4
dm_mirror button battery ac uhci_hcd ehci_hcd i2c_i801 i2c_core floppy
sd_mod ata_piix libata scsi_mod e1000 nfs lockd nfs_acl sunrpc
[ 2420.073140] Pid: 3400, comm: mdadm Not tainted 2.6.15 #2
[ 2420.107964] RIP: 0010:[]
{bitmap_create+1340}
[ 2420.155921] RSP: 0018:ffff810114e73a48 EFLAGS: 00010247
[ 2420.191887] RAX: 0000000000000000 RBX: ffff810117402c00 RCX:
0000000000000000
[ 2420.238702] RDX: 0000000000000fff RSI: 0000000000001000 RDI:
ffffffff804263a0
[ 2420.285516] RBP: ffff810114e73b28 R08: ffffffff804263b8 R09:
0000000000000000
[ 2420.332330] R10: 0000000100000000 R11: 0000000000000000 R12:
ffff810115110200
[ 2420.379143] R13: 0000000000000000 R14: 0000000000000000 R15:
0000000000200000
[ 2420.425958] FS: 00002aaaaaab4b00(0000) GS:ffffffff80528880(0000)
knlGS:0000000000000000
[ 2420.479051] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 2420.516732] CR2: 0000003eb298f070 CR3: 0000000114060000 CR4:
00000000000006e0
[ 2420.563546] Process mdadm (pid: 3400, threadinfo ffff810114e72000, task
ffff81011516a880)
[ 2420.617208] Stack: 0000000000000000 0000000000000000 0000000000000000
00000000000000fc
[ 2420.668591] 0000000000000000 0000000000000000 ffff810117402c00
0000000000000000
[ 2420.721113] 0000000000000000 0000000000000005
[ 2420.754226] Call Trace:{md_probe+177}
{do_md_run+1035}
[ 2420.808462] {bind_rdev_to_array+402}
{md_ioctl+5242}
[ 2420.865551] {__pagevec_free+46}
{release_pages+376}
[ 2420.922072] {find_get_pages+90}
{blkdev_driver_ioctl+91}
[ 2420.981445] {blkdev_ioctl+1745}
{kobject_put+25}
[ 2421.036252] {bdev_destroy_inode+31}
{destroy_inode+79}
[ 2421.094484] {generic_delete_inode+329}
{iput+124}
[ 2421.149862] {bdput+13}
{blkdev_put+411}
[ 2421.199530] {block_ioctl+27}
{do_ioctl+46}
[ 2421.250912] {vfs_ioctl+623}
{sys_ioctl+93}
[ 2421.302294] {system_call+126}
[ 2421.337689]
[ 2421.337690] Code: 0f 0b 68 4c d2 37 80 c2 38 06 49 89 4c 24 38 48 8b 55
80 be
[ 2421.394779] RIP {bitmap_create+1340} RSP

[ 2421.441946]


If I have to create RAID0 with bitmap support, what kind of mdadm
configuration I will have to use?

Thanks,
Yogesh

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Re: RAID0 with bitmap support in 2.6.15 kernel

On Monday April 17, pahilwan.yogesh@spsoftindia.com wrote:
> Hi Folks,
>
> I am creating RAID0 with bitmap support in 2.6.15 kernel.
>
> For that I have created 10GB partition each on 4 sata disks and try to
> created RAID0 over these 4 10 GB partitions and use one of the partitions on
> one of the disks for keeping the bitmap file. I have use following command
> for creating RAID0.
>
> # mdadm -Cv /dev/md0 -bitmap=/root/mntbitmap/RAID0.bitmap -bitmap-chunk=2048
> -l0 -n4 /dev/sd{a1,b1,c1,d1}
>
> But after this I am getting Segmentation fault and kernel oops as shown in
> dmesg.

Well, a Segmentation Fault certainly isn't good, and I will try to fix
it.
But bitmap support isn't available for raid0, because it is
meaningless.
The 'bitmap' records sections of the array which might be
inconsistent. As raid0 have no redundancy, it cannot be
inconsistent. So there is nothing to record.

What did you hope to gain by adding a bitmap to raid0??

NeilBrown
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