5 replies to this topic

[tinoy69]

I'm am new to this forum and would like to ask, i've recently experimenting with diskless technologies, and stumbled upon aoe by rebit, i've just experimented with winxp boot, and also researched well on the topic...

what my question is, is that some other diskless methods employs a write-back cache

1) i just want to understand what does a write-back cache do? i know it is used for iscsi diskless booting...
2) if i know the answer to 1) would it be possible to employ this into aoe?
3) do you know any other software like this to implement delayed caching to aoe? i'm thinking of deploying a single target in aoe to multiple workstations but it is said it can't be done due to the implementation of aoe...is this true?

Thanks for the enlightenment...

[Sha0]

...i'm thinking of deploying a single target in aoe to multiple workstations but it is said it can't be done due to the implementation of aoe...is this true?

Imagine that you have a hard disk drive that is somehow connected to multiple computers. Imagine that on that hard disk drive is a filesystem. Now imagine that the filesystem is not intended for simultaneous use by multiple systems. That is very similar to what you are talking about. Never use a single-computer filesystem with multiple computers at the same time if any of those computers are using the filesystem in a writable mode, or you will not enjoy the resulting corruption.

What you are probably more likely to enjoy is Copy-on-Write. Please see this article.

[tinoy69]

thank you for replying sha0

although i'm new to grasp the concept of what you have given...

there are other iscsi diskless system that have this cache software on both clients and servers...i do think the general purpose of that is that write operations on the single target is synchronized, so that it does not trashes the filesystem on the example you provided...i know in fact that aoe alone doesn't have this because you send direct hdd parameters over the packet which vblade directly talks to the target...

if i would have to imagine what i like to do is that

aoe client driver -> vblade cache (if there's such a thing) - vblade

so that whenever multiple devices access a target, all write's are temporarily cached so that when it is finally full, the cache finally dumps to vblade, which i hope won't cause corruption...

okay, if that's not possible, how is that other diskless systems (that employ iscsi), be able to use a single target booting multiple clients?

btw, sha0 can you please be so kind to point me to a tutorial on how to use your winvblock...thanks...also nice work on that...

[Sha0]

thank you for replying sha0

You're welcome to it.

...
there are other iscsi diskless system that have this cache software on both clients and servers...i do think the general purpose of that is that write operations on the single target is synchronized, so that it does not trashes the filesystem on the example you provided...

I'm afraid that you are mistaken. iSCSI deals with disks, not filesystems.

For example, you can have any disk filesystem you want to have, on a disk. You can even invent your own. Do you believe that some iSCSI product will know how to make sure your invented filesystem works nicely with multiple computers? Here is the problem: Suppose computer A reads the filesystem and says "the length of somefile.txt is 300 bytes." Then suppose computer B truncates somefile.txt so that it's only 42 bytes. Then suppose computer A tries to read the 300 bytes. This doesn't work. Delaying writes doesn't work either, since that results in a series of writes from multiple computers which do not make sense together.

i know in fact that aoe alone doesn't have this because you send direct hdd parameters over the packet which vblade directly talks to the target...

iSCSI is similar. iSCSI uses IP. AoE does not.

if i would have to imagine what i like to do is that

aoe client driver -> vblade cache (if there's such a thing) - vblade

so that whenever multiple devices access a target, all write's are temporarily cached so that when it is finally full, the cache finally dumps to vblade, which i hope won't cause corruption...

okay, if that's not possible, how is that other diskless systems (that employ iscsi), be able to use a single target booting multiple clients?

I already mentioned the answer at the bottom of my first response. If you were thinking of a particular product, I suppose you'd mention it... So you must be asking about the general strategy, instead.

btw, sha0 can you please be so kind to point me to a tutorial on how to use your winvblock...thanks...also nice work on that...

I don't know of any tutorial for WinVBlock. Maybe I've forgotten.

[tinoy69]

I already mentioned the answer at the bottom of my first response. If you were thinking of a particular product, I suppose you'd mention it... So you must be asking about the general strategy, instead.

right you are...okay, i'm not gonna mention any product...

okay let me cite another example...the use of gamedisk in diskless systems, the same gamedisk used by multiple workstations...
i mean if iscsi is similar to aoe in what you say (block device in windows), how come the concept of gamedisk that multiple workstation uses it (iscsi)? without any data corruption?

[Sha0]

okay let me cite another example...the use of gamedisk in diskless systems, the same gamedisk used by multiple workstations...
i mean if iscsi is similar to aoe in what you say (block device in windows), how come the concept of gamedisk that multiple workstation uses it (iscsi)? without any data corruption?

I already mentioned the answer at the bottom of my first response.