Re: Everchanging bytes at the end of mirror disks

11.12.2022 11:22, Warner Losh пишет:
>
>
> On Sat, Dec 10, 2022, 11:52 PM Artem Kuchin <artemkuchin76@gmail.com> 
> wrote:
>
>     Hello!
>
>     I am writing a small utility for myseld and part of it is comparing
>     gmirror disks. After running some tests i realized that some bytes at
>     the very end of disks are constantly changing.
>
>
> The last sector has metadata about the mirror and about the mirror 
> element.  It's this latter data that differs.
>
>
Looking  at  g_mirror.h

struct g_mirror_metadata {
         char            md_magic[16];   /* Magic value. */
         uint32_t        md_version;     /* Version number. */
         char            md_name[16];    /* Mirror name. */
         uint32_t        md_mid;         /* Mirror unique ID. */
         uint32_t        md_did;         /* Disk unique ID. */
         uint8_t         md_all;         /* Number of disks in mirror. */
         uint32_t        md_genid;       /* Generation ID. */
         uint32_t        md_syncid;      /* Synchronization ID. */
         uint8_t         md_priority;    /* Disk priority. */
         uint32_t        md_slice;       /* Slice size. */
         uint8_t         md_balance;     /* Balance type. */
         uint64_t        md_mediasize;   /* Size of the smallest
                                            disk in mirror. */
         uint32_t        md_sectorsize;  /* Sector size. */
         uint64_t        md_sync_offset; /* Synchronized offset. */
         uint64_t        md_mflags;      /* Additional mirror flags. */
         uint64_t        md_dflags;      /* Additional disk flags. */
         char            md_provider[16]; /* Hardcoded provider. */
         uint64_t        md_provsize;    /* Provider's size. */
         u_char          md_hash[16];    /* MD5 hash. */
};

 From this metadata seems like it is updated nearly each write: 
md_sync_offset (from g_mirror_sync_request), md_hash, maybe others. Poor 
last sector is written quadrillion times a day every day.

It does not look good to me, but maybe i am wrong? Also, does it mean no 
go for gmirror on ssd?

Artem