* question about ec partial read in a single stripe
@ 2017-11-09 11:10 zengran zhang
2017-11-09 12:50 ` zengran zhang
2017-11-09 14:30 ` Sage Weil
0 siblings, 2 replies; 3+ messages in thread
From: zengran zhang @ 2017-11-09 11:10 UTC (permalink / raw
To: ceph-devel
Hi all:
we found that partial read will cause full stripe read in now ec
impl, for example:
we have 4 chunks per stripe, 4K size per chunks and 16K per
stripe, when we read rand 2K in a stripe,the reads
will amplify to full stripe(16K +8K(Parity))..
i did not see any checksum or buffer related factor except the ec
extentcache.does the extentcache is the purpuse of the mechanism?
now we want increase the stripe width to improve the small random raed
performance, but the mechanism limit the result...
best regards!
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: question about ec partial read in a single stripe
2017-11-09 11:10 question about ec partial read in a single stripe zengran zhang
@ 2017-11-09 12:50 ` zengran zhang
2017-11-09 14:30 ` Sage Weil
1 sibling, 0 replies; 3+ messages in thread
From: zengran zhang @ 2017-11-09 12:50 UTC (permalink / raw
To: ceph-devel
i found a discuss on two years ago
(http://permalink.gmane.org/gmane.comp.file-systems.ceph.devel/23872)
and a pr commited by
XinzeChi(https://github.com/ceph/ceph/pull/4467)...
2017-11-09 19:10 GMT+08:00 zengran zhang <z13121369189@gmail.com>:
> Hi all:
> we found that partial read will cause full stripe read in now ec
> impl, for example:
> we have 4 chunks per stripe, 4K size per chunks and 16K per
> stripe, when we read rand 2K in a stripe,the reads
> will amplify to full stripe(16K +8K(Parity))..
>
> i did not see any checksum or buffer related factor except the ec
> extentcache.does the extentcache is the purpuse of the mechanism?
> now we want increase the stripe width to improve the small random raed
> performance, but the mechanism limit the result...
>
> best regards!
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: question about ec partial read in a single stripe
2017-11-09 11:10 question about ec partial read in a single stripe zengran zhang
2017-11-09 12:50 ` zengran zhang
@ 2017-11-09 14:30 ` Sage Weil
1 sibling, 0 replies; 3+ messages in thread
From: Sage Weil @ 2017-11-09 14:30 UTC (permalink / raw
To: zengran zhang; +Cc: ceph-devel
On Thu, 9 Nov 2017, zengran zhang wrote:
> Hi all:
> we found that partial read will cause full stripe read in now ec
> impl, for example:
> we have 4 chunks per stripe, 4K size per chunks and 16K per
> stripe, when we read rand 2K in a stripe,the reads
> will amplify to full stripe(16K +8K(Parity))..
Right.
> i did not see any checksum or buffer related factor except the ec
> extentcache.does the extentcache is the purpuse of the mechanism?
> now we want increase the stripe width to improve the small random raed
> performance, but the mechanism limit the result...
This is definitely an improvement we're interested in. I don't remember
what the issue with the previous PR was, but it appears to predate the EC
overwrites work (which merged about a year ago), so it will certainly need
to be reimplemented. The extentcache is there to support the
read/modify/write behavior for sub-stripe overwrites. Whatever we do for
small substripe reads will need to cooperate with that cache.
If you're interested in tackling this, that would be fantastic!
sage
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-11-09 11:10 question about ec partial read in a single stripe zengran zhang
2017-11-09 12:50 ` zengran zhang
2017-11-09 14:30 ` Sage Weil
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