I’m running OpenBSD on top of bHyve using virtual disks allocated out of ZFS
pools. While not the same setup, some concepts carry over…
I have two types of pools:
1) an “expensive" pool for fast random IO:
- this pool is made up stripes of SSD-based vdevs.
- ZFS is configured to use a 16K recordsize for this pool.
- good for small files (guest OS, DBs, web/mail/dns files, etc.)
- When ZFS is told to use the SSD, it starts the partition
on sector 256 (not the default sector 34) to ensure good
SSD NAND alignment.
2) a less-expensive pool for large sequential IO:
- this pool is a single RAIDZ2-based vdev using spinning rust.
- ZFS is configured to use a 1M recordsize for this pool.
- good for large files (movies, high-res images, backups, etc.)
Virtual disks are exposed to the OpenBSD guests from both pools. The guest’s
root-disk is always allocated from pool #1. Typically, a second
application-specific disk is also allocated from pool #1 (e.g., /var/www/sites
on a web server, /home on a mail server, etc.). Only in special circumstances
(e.g., a media server) is a disk allocated from pool #2.
This arrangement steps around needing to read/write 1M blocks for each small
file access, and also the possibility that a guest accessing a given block will
span more than a single physical block.
Can VMWare virtual disks be configured similarly?
K.
> On Apr 21, 2021, at 12:35 PM, Tom Smyth <tom.sm...@wirelessconnect.eu> wrote:
>
> Christian, Otto, Thanks for your feedback on this one....
>
> Ill research it further,
> but NTFS has 4K, 8K 32K and 64K Allocation units on the
> filessystem and for Microsoft windows running Exchange or Database workloads
> they were recommending alignment of the NTFS partitions
> on the 1MB offset also.
>
> From Otto's, explanation (Thanks) of 1/16 blocks would potentially
> cross a boundary of the
> storage subsystem,
> 6.25% of reads(or writes) could result in a double Read ( or double write)
>
> of course the write issue is a bigger problem for the SSDs..
>
> I can configure the partitions how I want ,for now anyway,
>
> Ill do a little digging on FFS and FFS2 and see how the filesystem
> database (or table)
> is structured...
>
> Thanks for the feedback it is very helpful to me....
>
> All the best,
>
> Tom Smyth
>
>
>
> On Wed, 21 Apr 2021 at 15:25, Christian Weisgerber <na...@mips.inka.de> wrote:
>>
>> Tom Smyth:
>>
>>> if you were to have a 1MB file or a database that needed to read 1MB
>>> of data, i
>>> f the partitions are not aligned then
>>> your underlying storage system need to load 2 chunks or write 2
>>> chunks for 1 MB of data, written,
>>
>> You seem to assume that FFS2 would align a 1MB file on an 1MB border
>> within the filesystem. That is not case. That 1MB file will be
>> aligned on a blocksize border (16/32/64 kB, depending on filesystem
>> size). Aligning the partition on n*blocksize has no effect on this.
>>
>> --
>> Christian "naddy" Weisgerber na...@mips.inka.de
>
>
>
> --
> Kindest regards,
> Tom Smyth.
>
