Discussion:
iSCSI question
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Greg
2024-09-16 16:50:02 UTC
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Hi there,

I would like ot use Debian box as iSCSI server (target if I'm not
wrong). So I have two questions:

1. If I export /dev/md0 via iSCSI would I benefit from memory buffers?

2. Is it possible to export a virtual device (like vmdk) by iSCSI? This
would allow slight overbooking of the storage space.

Thanks in advance for any help
Greg
Arno Lehmann
2024-09-16 19:30:02 UTC
Permalink
Hi Greg,
Post by Greg
Hi there,
I would like ot use Debian box as iSCSI server (target if I'm not
1. If I export /dev/md0 via iSCSI would I benefit from memory buffers?
That's an interesting question... in all environments I ever used it,
network was the bottleneck, so even if there are scenarios where memory
buffers may be useful, you'd need very good connectivity to notice them,
I think.
Post by Greg
2. Is it possible to export a virtual device (like vmdk) by iSCSI? This
would allow slight overbooking of the storage space.
vmdk in particular I don't know, but I have exported overcommitted /
thin LVs; for vmdk you might need to add some fancy losetup wrapper.

My experience with overcommitting block storage is not purely positive,
so I'd suggest to be very careful ;-)

Cheers,

Arno
Post by Greg
Thanks in advance for any help
Greg
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Greg
2024-09-17 07:50:02 UTC
Permalink
Post by Arno Lehmann
Hi Greg,
Post by Greg
Hi there,
I would like ot use Debian box as iSCSI server (target if I'm not
1. If I export /dev/md0 via iSCSI would I benefit from memory buffers?
That's an interesting question... in all environments I ever used it,
network was the bottleneck, so even if there are scenarios where memory
buffers may be useful, you'd need very good connectivity to notice them,
I think.
I'm using ConnectX 3pro Mellanox adapters (56Gbps), it was cheaper than
10Gb Ethernet.
Post by Arno Lehmann
Post by Greg
2. Is it possible to export a virtual device (like vmdk) by iSCSI?
This would allow slight overbooking of the storage space.
vmdk in particular I don't know, but I have exported overcommitted /
thin LVs; for vmdk you might need to add some fancy losetup wrapper.
My experience with overcommitting block storage is not purely positive,
so I'd suggest to be very careful ;-)
Ok, thanks
Andy Smith
2024-09-16 22:20:01 UTC
Permalink
Hi,
Post by Greg
1. If I export /dev/md0 via iSCSI would I benefit from memory buffers?
I've very little experience with iSCSI and don't know the answer to
this…
Post by Greg
2. Is it possible to export a virtual device (like vmdk) by iSCSI? This
would allow slight overbooking of the storage space.
…just want to say that I use qemu-nbd to turn things like vmdk
images into block devices, which I can then do anything with that I
do for other block devices, so that might be an option.

https://jasonmurray.org/posts/2021/mountvmdk/

Thanks,
Andy
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Greg
2024-09-17 08:00:01 UTC
Permalink
Post by Andy Smith
Hi,
Post by Greg
1. If I export /dev/md0 via iSCSI would I benefit from memory buffers?
I've very little experience with iSCSI and don't know the answer to
this…
Post by Greg
2. Is it possible to export a virtual device (like vmdk) by iSCSI? This
would allow slight overbooking of the storage space.
…just want to say that I use qemu-nbd to turn things like vmdk
images into block devices, which I can then do anything with that I
do for other block devices, so that might be an option.
https://jasonmurray.org/posts/2021/mountvmdk/
Thanks for the tip. it seems quite natural idea to use virtual drives.
Is there any tgtd "plugin" or "driver" with virtual disk support?
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