On 2016/04/25, 09:36, "Chris Hunter" <chuntera(a)gmail.com> wrote:
To follow-up about 4k sector drives.
How much on-disk space would ldiskfs MDT inodes use on 4k sector
The same as they always do. The 4KB sector size is the minimum IO size,
and matches the default blocksize used for all ldiskfs filesystems.
ldiskfs will pack multiple inodes into one block as you write below.
For example the LOM limits has 2TB ldiskfs MDT volume = 1 billion
inodes, which is based on 2k inode sizes.
Would each 2k entry in the MDT inode table occupy a 4k drive sector?
To clarify this further, the "2KB per inode" is not the actual size of
the inode, but rather the ratio of space per inode used at format time.
The inode size is 512 bytes per inode, so 8 inodes are packed into a 4KB
block. The remaining 1.5KB per inode is for things like directory
blocks, xattr blocks for files with more stripes than can fit into the
inode (7 or more stripes in most cases), and Lustre internal metadata
like ChangeLogs, Object Index (OI) files, recovery logs, etc.
I added more details in my patch http://review.whamcloud.com/19786
"LUDOC-331 setup: explain ldiskfs inode size/ratio better"
To answer my own question, from the ext4 wiki, I believe inode table
a "packed" data structure to make efficient use of file blocks.
On Tue, 2016-04-05 at 21:35 +0000, Dilger, Andreas wrote:
> Both ldiskfs and ZFS work well with 4KB sector drives, since this is
>already very common for deployment. Ldiskfs is always using 4KB
> One caveat for ZFS is that if such drives misrepresent themselves as
>512-byte drives it is necessary to specify "ashift=12" at pool creation
>time to set the minimum block size to 2^12 = 4096 bytes, otherwise the
>512-byte emulation in the drive will hurt ZFS performance significantly.
> Cheers, Andreas
> > On Apr 5, 2016, at 08:07, Chris Hunter <chuntera(a)gmail.com> wrote:
> > Are there any potential issues with using 4k sector (aka "advanced
> > format") disk drives with Lustre ?
> > Most Lustre implementations would use RAID arrays. I recognize there
> > be changes necessary in RAID chunk/stripe settings with 4k drives.
> > since lustre does not recommend using drive parition tables, there
> > should not be a problem with partition alignment.
> > Are there changes required at lfdiskfs or zfs level ?
> > regards,
> > chris hunter
> > chuntera(a)gmail.com
> > _______________________________________________
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> > HPDD-discuss(a)lists.01.org
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Lustre Principal Architect
Intel High Performance Data Division