Alignment at the CoreStorage LVM layer, ashift above?

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Alignment at the CoreStorage LVM layer, ashift above?

Post by grahamperrin » Thu Oct 18, 2012 12:06 pm

Seagate Momentus® XT ST750LX003-1AC154 solid state hybrid – not explicitly Advanced Format at http://www.seagate.com/gb/en/internal-h ... rd-drives/ but 4,096 Bytes per sector for ST750LX003 in the data sheet.

ashift is 0 but in this case I'm not rushing to recreate the pool with
ashift=12 because there's CoreStorage (logical volume management) between the pool and the disk.

I guess that if alignment is proper at the (lower) CoreStorage layer, then I can accept the default ashift 0 at the (upper) ZFS pool layer.

True?

No rush for an answer. (I don't expect other people to experiment with CoreStorage in this way.)

Code: Select all
macbookpro08-centrim:~ gjp22$ zpool get ashift gjp22
NAME   PROPERTY  VALUE   SOURCE
gjp22  ashift    0       default
macbookpro08-centrim:~ gjp22$ zpool list
NAME     SIZE   ALLOC    FREE     CAP  HEALTH  ALTROOT
gjp22   572Gi   377Gi   195Gi     65%  ONLINE  -
macbookpro08-centrim:~ gjp22$ zfs list
NAME     USED   AVAIL   REFER  MOUNTPOINT
gjp22   377Gi   186Gi   327Gi  /Volumes/gjp22
macbookpro08-centrim:~ gjp22$ diskutil list disk2
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *616.0 GB   disk2
   1:                        EFI                         209.7 MB   disk2s1
   2:                        ZFS                         615.7 GB   disk2s2
macbookpro08-centrim:~ gjp22$ diskutil coreStorage list
CoreStorage logical volume groups (2 found)
|
+-- Logical Volume Group 902434C9-0131-4E3A-AE15-2B8B938087AD
|   =========================================================
|   Name:         gjp22-cs
|   Size:         616336003072 B (616.3 GB)
|   Free Space:   0 B (0 B)
|   |
|   +-< Physical Volume 179AADE6-34F1-404C-A994-9FD99C881BA6
|   |   ----------------------------------------------------
|   |   Index:    0
|   |   Disk:     disk0s7
|   |   Status:   Online
|   |   Size:     616336003072 B (616.3 GB)
|   |
|   +-> Logical Volume Family FFCE2FAF-BE8E-4FEF-9F3E-E221C6CBCA11
|       ----------------------------------------------------------
|       Encryption Status:       Unlocked
|       Encryption Type:         AES-XTS
|       Conversion Status:       Complete
|       Conversion Direction:    -none-
|       Has Encrypted Extents:   Yes
|       Fully Secure:            Yes
|       Passphrase Required:     Yes
|       |
|       +-> Logical Volume 0CFAFD38-E79B-40AC-A4BE-63296E6B4331
|           ---------------------------------------------------
|           Disk:               disk2
|           Status:             Online
|           Size (Total):       616017227776 B (616.0 GB)
|           Size (Converted):   -none-
|           Revertible:         No
|           LV Name:            gjp22-cs
|           Content Hint:       Apple_HFS
|
+-- Logical Volume Group 039C0D47-F3CF-44D3-A825-B48F01FCF334
    =========================================================
    Name:         OS
    Size:         99484213248 B (99.5 GB)
    Free Space:   0 B (0 B)
    |
    +-< Physical Volume 86D2FA98-8C69-4828-B909-8312AE4A75E2
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk0s5
    |   Status:   Online
    |   Size:     99484213248 B (99.5 GB)
    |
    +-> Logical Volume Family 7AA96B8E-0E41-4C3F-9589-5FAE0C956372
        ----------------------------------------------------------
        Encryption Status:       Unlocked
        Encryption Type:         AES-XTS
        Conversion Status:       Complete
        Conversion Direction:    -none-
        Has Encrypted Extents:   Yes
        Fully Secure:            Yes
        Passphrase Required:     Yes
        |
        +-> Logical Volume B13EE5BF-5D08-49D3-94C2-DF58AFEA1D08
            ---------------------------------------------------
            Disk:               disk1
            Status:             Online
            Size (Total):       99165437952 B (99.2 GB)
            Size (Converted):   -none-
            Revertible:         No
            LV Name:            OS
            Volume Name:        OS
            Content Hint:       Apple_HFS
macbookpro08-centrim:~ gjp22$
grahamperrin Offline

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Re: Alignment at the CoreStorage LVM layer, ashift above?

Post by si-ghan-bi » Thu Oct 18, 2012 3:14 pm

Apparently I don't have CoreStorage in use. Strange.
Did you activate it on purpose?
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Re: Alignment at the CoreStorage LVM layer, ashift above?

Post by grahamperrin » Thu Oct 18, 2012 7:49 pm

I use CoreStorage for encryption.
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Re: Alignment at the CoreStorage LVM layer, ashift above?

Post by grahamperrin » Wed Oct 24, 2012 10:32 pm

I forgot to mention the layer that's probably more relevant than CoreStorage LVM: GPT.

Partitioning of the internal disk was performed a few months ago, probably with Disk Utility whilst booted from Recovery OS 10.8 (on a USB flash drive). AFAIR I chose to encrypt the LVs at the times of their creation – before installing the OS.

Frequently Asked Questions about MacZFS: What should I do with 4k (Advanced Format) hard drives? reminds me:

… The following is partially an opinion piece, and I invite correction and clarity.

If you create your partitions … using Disk Utility …, then the system automatically aligns everything to 4k blocks. Then, you create your zpool. …


– plus in my case, an additional step of creating CoreStorage logical volumes before creating the ZFS pool within one of the LVs.

So (answering my own question, unless anyone thinks otherwise):

  • in this case, default ashift 0 at the ZFS pool layer is OK.
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