On 07/29/2012 04:07 PM, Jim Klimov wrote:
> Hello, list
> For several times now I've seen statements on this list implying
> that a dedicated ZIL/SLOG device catching sync writes for the log,
> also allows for more streamlined writes to the pool during normal
> healthy TXG syncs, than is the case with the default ZIL located
> within the pool.
> Is this understanding correct? Does it apply to any generic writes,
> or only to sync-heavy scenarios like databases or NFS servers?
Yes, it is correct. It applies to all writes. If the log is allocated on
a slog devices, then the synchronous log records don't fragment the
pool. As far as I understand it, txgs happen sequentially even with no
slog device present, but the log entries don't - they occur as is needed
to fulfill the sync write request with minimum latency.
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